ASTM C591-22

Standard Specification for Unfaced Preformed Rigid Cellular Polyisocyanurate Thermal Insulation

ABSTRACT
This specification covers the types, physical properties, and dimensions of unfaced, preformed rigid cellular polyurethane modified polyisocyanurate plastic material intended for use as thermal insulation on surfaces. This insulation can be classified into six types according to its compressive resistance: Types I, IV, II, III, V, and VI. Also this insulation can be classified as Grades 1 and 2 according to its service temperature range. The thermal insulation is produced by the polymerization of polymeric polyisocyanates in the presence of polyhydroxyl compounds, catalysts, cell stabilizers, and blowing agents. Different test methods shall be performed in order to determine the thermal insulation's following properties: density, compressive resistance, apparent thermal conductivity, hot-surface performance, water absorption, water vapor permeability, dimensional stability, closed-cell content, surface bearing characteristics, tensile strength, and leachable chloride, fluoride, silicate, and sodium ions.
SCOPE
1.1 This specification covers the types, physical properties, and dimensions of unfaced, preformed rigid cellular polyisocyanurate plastic material intended for use as thermal insulation on surfaces from –297°F (–183°C) to 300°F (149°C). For specific applications, the actual temperature limits shall be agreed upon by the manufacturer and purchaser.  
1.2 This specification only covers “polyurethane modified polyisocyanurate” thermal insulation which is commonly referred to as “polyisocyanurate” thermal insulation. This standard does not encompass all polyurethane modified materials. Polyurethane modified polyisocyanurate and other polyurethane materials are similar, but the materials will perform differently under some service conditions.  
1.3 This standard is designed as a material specification, not a design document. Physical property requirements vary by application and temperature. At temperatures below –70°F (–51°C) the physical properties of the polyisocyanurate insulation at the service temperature are of particular importance. Below –70°F (–51°C) the manufacturer and the purchaser must agree on what additional cold temperature performance properties are required to determine if the material can function adequately for the particular application.  
1.4 This standard addresses requirements of unfaced preformed rigid cellular polyisocyanurate thermal insulation manufactured using blowing agents with an ozone depletion potential of 0 (ODP 0).  
1.5 Except 6.2 and 8.2 – 8.4, which are related to the size and shape of fabricated parts, and 16.1, which is related to the storage of fabricated parts, the requirements in this standard specification apply to the polyisocyanurate insulation in the form of buns supplied by the insulation manufacturer.  
1.6 When adopted by an authority having jurisdiction, codes that address fire properties in many applications regulate the use of the thermal insulation materials covered by this specification. Fire properties are controlled by job, project, or other specifications where codes or government regulations do not apply.  
1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2022
• ICS: 83.100 - Cellular materials
• ICS: 91.100.60 - Thermal and sound insulating materials
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.22 - Organic and Nonhomogeneous Inorganic Thermal Insulations

Relations

• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM E96/E96M-24 - Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
• Effective Date: 01-Mar-2024
• Refers: ASTM C1363-24 - Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus
• Effective Date: 01-Mar-2024
• Refers: ASTM C390-08(2024) - Standard Practice for Sampling and Acceptance of Thermal Insulation Lots
• Effective Date: 01-Mar-2024
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM E84-23d - Standard Test Method for Surface Burning Characteristics of Building Materials
• Effective Date: 01-Dec-2023
• Refers: ASTM E96/E96M-23 - Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
• Effective Date: 15-Nov-2023
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM C1303/C1303M-23 - Standard Test Method for Predicting Long-Term Thermal Resistance of Closed-Cell Foam Insulation
• Effective Date: 01-Nov-2023
• Refers: ASTM E84-23c - Standard Test Method for Surface Burning Characteristics of Building Materials
• Effective Date: 01-Sep-2023
• Refers: ASTM C1763-20 - Standard Test Method for Water Absorption by Immersion of Thermal Insulation Materials
• Effective Date: 01-May-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM C1763-19e1 - Standard Test Method for Water Absorption by Immersion of Thermal Insulation Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM C1763-19 - Standard Test Method for Water Absorption by Immersion of Thermal Insulation Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM C390-08(2019) - Standard Practice for Sampling and Acceptance of Thermal Insulation Lots
• Effective Date: 01-Sep-2019

Overview

ASTM C591-22, published by ASTM International, specifies the requirements for unfaced preformed rigid cellular polyisocyanurate thermal insulation. This standard covers the types, physical properties, and dimensional tolerances for this insulation material, which is commonly used for thermal insulation on various surfaces operating in temperature ranges from –297°F (–183°C) up to 300°F (149°C). The specification primarily addresses properties relevant to material performance, quality assurance, and product classification. The material is manufactured using polymeric polyisocyanurate, ensuring it has a zero ozone depletion potential (ODP).

Key Topics

• Material Types & Classification:
  Polyisocyanurate insulation under this standard is classified into six types according to compressive resistance (Types I, IV, II, III, V, VI). Each type is defined by minimum density and strength requirements, ensuring suitability for specific loads and applications.

• Physical Properties & Performance:
  The specification establishes requirements for:

  • Density and Compressive Strength
  • Apparent Thermal Conductivity
  • Water Absorption
  • Water Vapor Permeability
  • Dimensional Stability
  • Closed-Cell Content
  • Hot-Surface Performance

• Service Temperature:
  The covered grade (Grade 2) is suitable for service temperatures between –297°F (–183°C) and 300°F (149°C). Applications requiring performance outside this temperature range should be negotiated with the manufacturer.

• Fabrication and Tolerances:
  Polyisocyanurate insulation is supplied in large "bun" forms. Fabricators cut the buns to produce boards, pipe shells, or custom shapes. Dimensional tolerances for length, width, thickness, edge trueness, and squareness are defined to ensure fit and thermal performance.

• Testing and Quality Assurance:
  The standard references numerous ASTM test methods to verify required properties, including ASTM C165 (compressive properties), ASTM C177 (thermal conductivity), and ASTM D1622 (density measurement).

• Fire and Safety Considerations:
  The material is combustible and not to be installed near flames. Compliance with building codes and fire safety regulations is essential. Fire performance is addressed by additional project or regulatory specifications as required.

• Environmental Responsibility:
  Only blowing agents with ODP 0 may be used in manufacturing, supporting compliance with environmental and sustainability directives.

Applications

ASTM C591-22 polyisocyanurate thermal insulation is widely used in industrial, commercial, and building construction sectors. Typical applications include:

• Insulation for piping, ducts, tanks, and vessels in power plants and chemical processing facilities
• Building envelope insulation for walls, roofs, and floors
• Refrigeration equipment and cold storage units
• Insulation for process equipment exposed to cryogenic or high-temperature conditions

This standard supports the selection of high-performance, durable insulation products for energy efficiency, condensation control, and process stability.

Related Standards

To ensure comprehensive quality and compatibility, ASTM C591-22 cites and should be used in conjunction with several other ASTM standards, including:

• ASTM C168 - Terminology Relating to Thermal Insulation
• ASTM D1622 - Test Method for Density of Rigid Cellular Plastics
• ASTM C177 & C518 - Test Methods for Thermal Transmission Properties
• ASTM C585 - Dimensional Practices for Pipe and Tubing Insulation
• ASTM C411 - Test Method for Hot-Surface Performance
• ASTM E96 - Water Vapor Transmission Rate Testing
• ASTM C390 - Sampling and Acceptance

Users should refer to these and related standards for guidance on testing procedures, installation, and long-term product performance.

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Keywords: ASTM C591-22, polyisocyanurate insulation, rigid cellular insulation, thermal insulation standards, building insulation, industrial insulation, thermal conductivity, material specification, zero ozone depletion potential, thermal performance, ASTM thermal insulation standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C591 −22
Standard Specification for
Unfaced Preformed Rigid Cellular Polyisocyanurate Thermal
Insulation
This standard is issued under the fixed designation C591; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 1.6 Whenadoptedbyanauthorityhavingjurisdiction,codes
that address fire properties in many applications regulate the
1.1 This specification covers the types, physical properties,
use of the thermal insulation materials covered by this speci-
and dimensions of unfaced, preformed rigid cellular polyiso-
fication. Fire properties are controlled by job, project, or other
cyanurate plastic material intended for use as thermal insula-
specifications where codes or government regulations do not
tion on surfaces from –297°F (–183°C) to 300°F (149°C). For
apply.
specific applications, the actual temperature limits shall be
1.7 The values stated in inch-pound units are to be regarded
agreed upon by the manufacturer and purchaser.
as standard. The values given in parentheses are mathematical
1.2 This specification only covers “polyurethane modified
conversions to SI units that are provided for information only
polyisocyanurate” thermal insulation which is commonly re-
and are not considered standard.
ferred to as “polyisocyanurate” thermal insulation. This stan-
1.8 This standard does not purport to address all of the
dard does not encompass all polyurethane modified materials.
safety concerns, if any, associated with its use. It is the
Polyurethane modified polyisocyanurate and other polyure-
responsibility of the user of this standard to establish appro-
thane materials are similar, but the materials will perform
priate safety, health, and environmental practices and deter-
differently under some service conditions.
mine the applicability of regulatory limitations prior to use.
1.3 This standard is designed as a material specification, not
1.9 This international standard was developed in accor-
a design document. Physical property requirements vary by
dance with internationally recognized principles on standard-
application and temperature. At temperatures below –70°F
ization established in the Decision on Principles for the
(–51°C) the physical properties of the polyisocyanurate insu-
Development of International Standards, Guides and Recom-
lation at the service temperature are of particular importance.
mendations issued by the World Trade Organization Technical
Below–70°F(–51°C)themanufacturerandthepurchasermust
Barriers to Trade (TBT) Committee.
agree on what additional cold temperature performance prop-
erties are required to determine if the material can function 2. Referenced Documents
adequately for the particular application. 2
2.1 ASTM Standards:
C165 Test Method for Measuring Compressive Properties of
1.4 This standard addresses requirements of unfaced pre-
Thermal Insulations
formed rigid cellular polyisocyanurate thermal insulation
C168 Terminology Relating to Thermal Insulation
manufactured using blowing agents with an ozone depletion
C177 Test Method for Steady-State Heat Flux Measure-
potential of 0 (ODP 0).
ments and Thermal Transmission Properties by Means of
6.2 and 8.2 – 8.4, which are related to the size
1.5 Except
the Guarded-Hot-Plate Apparatus
and shape of fabricated parts, and 16.1, which is related to the
C272/C272M Test Method for Water Absorption of Core
storage of fabricated parts, the requirements in this standard
Materials for Sandwich Constructions
specification apply to the polyisocyanurate insulation in the
C303 Test Method for Dimensions and Density of Pre-
form of buns supplied by the insulation manufacturer.
formed Block and Board–Type Thermal Insulation
C335/C335M Test Method for Steady-State Heat Transfer
Properties of Pipe Insulation
This specification is under the jurisdiction of ASTM Committee C16 on
Thermal Insulation and is the direct responsibility of Subcommittee C16.22 on
Organic and Nonhomogeneous Inorganic Thermal Insulations. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2022. Published December 2022. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1966. Last previous edition approved in 2021 as C591 – 21. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C0591-22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C591 − 22
C390 Practice for Sampling and Acceptance of Thermal 3.4.1.1 Discussion—Unfacedpreformedrigidcellularpolyi-
Insulation Lots socyanurate thermal insulation samples are aged because the
C411 Test Method for Hot-Surface Performance of High- thermal conductivity of this material increases with time,
Temperature Thermal Insulation primarily due to changes in the composition of the gas
C518 Test Method for Steady-State Thermal Transmission contained within the closed cells. The rate of this thermal
Properties by Means of the Heat Flow Meter Apparatus conductivity increase diminishes with time so an aging time
C550 Test Method for Measuring Trueness and Squareness priortotestingisselectedtoreasonablyrepresentthelong-term
of Rigid Block and Board Thermal Insulation performance of the material. The aging time for thermal
C585 Practice for Inner and Outer Diameters of Thermal conductivity test specimens of material covered by this stan-
Insulation for Nominal Sizes of Pipe and Tubing dard is typically 180 days.
C871 Test Methods for ChemicalAnalysis of Thermal Insu-
3.4.2 conditioned, v—the act of putting specimens in speci-
lationMaterialsforLeachableChloride,Fluoride,Silicate,
fied temperature and humidity conditions immediately prior to
and Sodium Ions
testing to allow the specimens to reach temperature and
C1045 Practice for Calculating Thermal Transmission Prop-
moisture content equilibrium.
erties Under Steady-State Conditions
3.4.2.1 Discussion—Samples are conditioned for a fairly
C1058/C1058M Practice for Selecting Temperatures for
short time period (typically 12 to 24 h) during which the test
Evaluating and Reporting Thermal Properties of Thermal
lab holds the sample at standard lab conditions (see 11.3)
Insulation
immediately prior to testing. If specimens are aged (see 3.4.1)
C1114 Test Method for Steady-State Thermal Transmission
for thermal conductivity testing at the same conditions speci-
Properties by Means of the Thin-Heater Apparatus
fied for conditioning and kept at these conditions until the time
C1303/C1303M Test Method for Predicting Long-Term
of testing, then a separate conditioning period at the end of the
Thermal Resistance of Closed-Cell Foam Insulation
aging period is not necessary.
C1363 Test Method for Thermal Performance of Building
3.4.3 final polymerization, n—the final chemical reaction
Materials and Envelope Assemblies by Means of a Hot
and cooling that occurs immediately following primary manu-
Box Apparatus
facturing of unfaced preformed rigid cellular polyisocyanurate
C1763 Test Method for Water Absorption by Immersion of
thermal insulation materials created using a simultaneous
Thermal Insulation Materials
blowing and exothermic polymerization process.
D883 Terminology Relating to Plastics
3.4.3.1 Discussion—Unfacedpreformedrigidcellularpolyi-
D1621 Test Method for Compressive Properties of Rigid
socyanurate thermal insulation materials created using a simul-
Cellular Plastics
taneous blowing and exothermic polymerization process are
D1622/D1622M Test Method forApparent Density of Rigid
formed into a shape such as a bun during manufacture. This
Cellular Plastics
shape reaches its final form and size during primary manufac-
D2126 Test Method for Response of Rigid Cellular Plastics
turingandisatatemperaturesubstantiallyaboveambient.This
to Thermal and Humid Aging
shape continues to undergo final polymerization and cooling
D2856 Test Method for Open-Cell Content of Rigid Cellular
foratimeperiodrangingfromafewhourstoseveraldays.This
Plastics by the Air Pycnometer (Withdrawn 2006)
period of final polymerization and cooling is part of the
D6226 Test Method for Open Cell Content of Rigid Cellular
manufacturing process and samples are not taken for testing or
Plastics
quality control until the end of this period is reached.
E84 Test Method for Surface Burning Characteristics of
Building Materials 3.4.4 insulation fabricator, n—a company that machines,
E96/E96M Test Methods for Gravimetric Determination of
cuts, grinds, or otherwise transforms the unfaced polyisocya-
Water Vapor Transmission Rate of Materials nurate bun insulation received from an insulation manufacturer
into various shapes such as boards, blocks, pipe shells, tank
3. Terminology
segments, and elbows/fittings.
3.1 For descriptions of terms used in this specification, refer
3.4.4.1 Discussion—It is possible for a company to function
to Terminologies C168 and D883.
as both an insulation fabricator and an insulation manufacturer.
In this standard specification the insulation fabricator is also
3.2 The term polyisocyanurate does not encompass all
referred to simply as the fabricator.
polyurethane containing materials (see 1.2).
3.4.5 insulation manufacturer, n—a company engaged in
3.3 The term “core specimen” refers to representative
primary manufacturing of unfaced polyisocyanurate foam.
samples cut in accordance with the sampling procedure listed
3.4.5.1 Discussion—It is possible for a company to function
within each property test method.
as both an insulation manufacturer and an insulation fabricator.
3.4 Definitions of Terms Specific to This Standard:
In this standard specification the insulation manufacturer is
3.4.1 aged, v—in relation to thermal conductivity testing,
also referred to simply as the manufacturer.
the act of delaying thermal conductivity testing for a specified
3.4.6 ozone depletion potential (ODP), n—a relative index
time period after the final polymerization.
indicating the extent to which a chemical product causes ozone
3 depletion.
The last approved version of this historical standard is referenced on
www.astm.org. 3.4.6.1 Discussion—The reference level of 1 is the potential
C591 − 22
of trichlorofluoromethane (R-11 or CFC-11) to cause ozone the average from testing the number of test specimen(s)
depletion. ODP 0 is an ozone depletion potential of zero. requiredby11.4 ofthisspecificationshall beusedtodetermine
compliance.
3.4.7 primary manufacturing, n—the initial manufacturing
step of unfaced preformed rigid cellular polyisocyanurate
NOTE 1—It is the responsibility of the user of this standard to determine
thermal insulation materials that begins with the mixing of the
the technical requirements for their specific applications and to select an
appropriate Type of material.
precursor chemicals and ends with the formation of the final
bun shape.
7.2 Polyisocyanurate thermal insulation is an organic mate-
rial and is combustible. Do not expose this insulation to flames
4. Classification
or other ignition sources. The fire performance of the material
4.1 Unfaced,preformedrigidcellularpolyisocyanuratether-
shall be addressed through fire test requirements established by
malinsulationcoveredbythisspecificationisclassifiedintosix
the appropriate governing authority. The manufacturer shall be
types as follows:
contacted for specific data as fire performance characteristic
4.1.1 Type I—Compressive resistance of 20 lb/in (137
will vary with grade, type, and thickness.
kPa), minimum.
2 7.3 Not all physical properties at temperatures below -70°F
4.1.2 Type IV—Compressive resistance of 22 lb/in (150
(-51°C) have been fully tested. Where these properties are
kPa), minimum.
2 critical, the user shall consult the manufacturer for properties
4.1.3 Type II—Compressive resistance of 35 lb/in (240
and performance at these lower temperatures.
kPa), minimum.
4.1.4 Type III—Compressive resistance of 45 lb/in (310
8. Dimensions and Tolerances
kPa), minimum.
4.1.5 Type V—Compressive resistance of 80 lb/in (550
8.1 The polyisocyanurate bun dimensions shall be as agreed
kPa), minimum.
upon by the purchaser and the manufacturer. Polyisocyanurate
4.1.6 Type VI—Compressive resistance of 125 lb/in (862
buns are commonly available in lengths up to 144 in. (3.66 m),
kPa), minimum.
widths up to 48 in. (1.22 m), and thicknesses from 12 in. (305
mm) to 24 in. (610 mm).
4.2 Unfaced,preformedrigidcellularpolyisocyanuratether-
mal insulation covered by this specification is classified into
8.2 Insulation Board (cut from buns by a fabricator):
one grade as follows:
8.2.1 Dimensional tolerances for boards shall be as follows:
4.2.1 Grade 2–Service temperature range of -297°F
Dimension Tolerance, in. (mm)
(-183°C) to 300°F (149°C).
Length ± ⁄8 (3.2)
Width ± ⁄16 (1.6)
Thickness ± ⁄32 (0.8)
5. Ordering Information
8.2.2 Edge Trueness—Determine in accordance with Test
5.1 Orders for materials purchased under this specification
Method C550.The maximum deviation from the edge trueness
shall include the following:
shall not be greater than ⁄32 in./ft (2.6 mm/m) of length or
5.1.1 Designation of this specification and year of issue,
width.
5.1.2 Product name or grade/type, or both,
5.1.3 Apparent thermal conductivity and specific thickness 8.2.3 Face Trueness—Determine in accordance with Test
required,
Method C550. The maximum deviation from flatness shall not
5.1.4 Product dimensions, be greater than ⁄16 in./ft (5.2 mm/m) of length or width.
5.1.5 Quantity of material,
8.2.4 Corner Squareness—Determine in accordance with
5.1.6 Special packaging or marking, if required, and
Test Method C550. The maximum deviation from corner
5.1.7 Special requirements for inspection or testing, or both. 1
squareness shall not be greater than ⁄8 in. (3.2 mm) for all
board thicknesses.
6. Materials and Manufacture
8.2.5 Edge Squareness—Determine in accordance with Test
6.1 Unfaced,preformedrigidcellularpolyisocyanuratether-
Method C550. The maximum deviation from edge squareness
mal insulation is produced by the polymerization of polymeric
shall not be greater that ⁄16 in. (1.6 mm) for all board
polyisocyanates in the presence of polyhydroxyl compounds,
thicknesses.
catalysts, cell stabilizers, and blowing agents.
8.3 Pipe Insulation (cut from buns by a fabricator)—
6.2 The material covered by this specification shall be
Materialsuppliedforpipeinsulationshallhavedimensionsand
supplied in “bun” form by the manufacturer. From these buns,
tolerances that are in accordance with Practice C585.
a fabricator shall transform and supply boards, blocks, pipe
8.4 Other parts or special shapes (cut from buns by a
shells, tank segments, elbows/fittings, or special shapes as
fabricator) shall have dimensions and tolerances agreed upon
agreed upon by the fabricator and end-user.
by the purchaser and fabricator.
7. Physical Properties
9. Workmanship and Appearances
7.1 Unfaced,preformedrigidcellularpolyisocyanuratether-
mal insulation shall conform to the requirements shown in 9.1 The polyisocyanurate thermal insulation shall have no
Table 1. See Note 1. For each physical property requirement, defects that will adversely affect its service qualities.
C591 − 22
TABLE 1 Physical Property Requirements
A
Grade 2: Operating Temperature Range -297°F (-183°C) to 300°F (149°C)
NOTE 1—Grade 1, which was specific to PIR for use at operating temperatures of -70°F (-51°C) to 300°F (149°C) , was deleted in 2009 because this
material was no longer produced. Grade 2 was not renumbered to minimize conflict with various global engineering and end-user specifications which
require the use of materials complying with, “ASTM C591, Grade 2”.
Property Type I Type IV Type II Type III Type V Type VI
3 3
Density, min lb/ft (kg/m ) 1.8 (29) 2.0 (32) 2.5 (40) 3.0 (48) 4.0 (60) 6.0 (96)
Compressive resistance at 10 % deformation 20 (137) 22 (150) 35 (240) 45 (310) 80 (550) 125 (862)
or yield whichever occurs first, parallel to
rise, min, lb/in (kPa)
Apparent thermal conductivity, max
Btu-in/h-ft -°F (W/m-K),
at a mean temperature of:
-200°F (-129°C) .13 (.019) .13 (.019) .13 (.019) .14 (.020) .14 (.020) .15 (.022)
-150°F (-101°C) .15 (.022) .15 (.022) .15 (.022) .16 (.023) .16 (.023) .17 (.025)
-100°F (-73°C) .17 (.025) .17 (.025) .17 (.025) .18 (.026) .18 (.026) .19 (.027)
-50°F (-46°C) .19 (.027) .19 (.027) .19 (.027) .20 (.029) .20 (.029) .21 (.030)
0°F (-17°C) .19 (.027) .19 (.027) .19 (.027) .20 (.029) .20 (.029) .22 (.032)
50°F (10°C) .18 (.026) .18 (.026) .18 (.026) .19 (.027) .19 (.027) .21 (.030)
75°F (24°C) .19 (.027) .19 (.027) .19 (.027) .20 (.029) .20 (.029) .22 (.032)
150°F (66°C) .23 (.033) .23 (.033) .23 (.033) .24 (.035) .24 (.035) .26 (.037)
200°F (93°C) .26 (.037) .26 (.037) .26 (.037) .27 (.039) .27 (.039) .30 (.044)
Water absorption, max, % by volume 2.0 2.0 1.0 1.0 1.0 0.8
Water vapor permeability, max, perm-in (ng/Pa-s-m) 4.0 (5.8) 4.0 (5.8) 3.5 (5.1) 3.0 (4.4) 2.5 (3.7) 2.0 (2.9)
Dimensional stability, max % linear change, 1 week exposure
158 ± 4°F (70 ± 2°C), 97 + 3 % relative humidity 4 4 4 4 4 4
-40 ± 6°F (-40 ± 3°C), ambient relative humidity 1 1 1 1 1 1
212 ± 4°F (100 ± 2°C), ambient relative humidity 2 2 2 2 2 2
Closed cell content, min 90 90 90 90 90 90
B
Hot-surface performance, at 300°F (149°C) Pass Pass Pass Pass Pass Pass
A
Thisspecificationdoesnotpurporttoaddressalltheperformanceissuesassociatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappropriate
performance criteria.
B
Pass ⁄fail criteria found in 12.4.
10. Sampling 11.3 Unless otherwise specified, the test specimens shall be
conditioned (see 3.4.2)at73 6 4°F (23 6 2°C) and 50 65%
10.1 Unless otherwise specified, the polyisocyanurate ther-
relative humidity for at least 24 h prior to testing.
malinsulationshallbesampledandinspectedforacceptanceof
material in accordance with Practice C390.
11.4 Numberofspecimenstotestforeachrequiredproperty
for continuous bunstock PIR (see A1.2):
10.2 Inspection Requirements—The requirements for den-
11.4.1 Density—Test three specimens.
sity shown in Table 1, the dimensional requirements described
11.4.2 Compressive Resistance—Test six specimens.
in Section 8, and the workmanship and appearance require-
11.4.3 Apparent Thermal Conductivity—Test three speci-
ments described in Section 9 are defined as inspection require-
mens at mean temperature of 75°F (24°C) and one specimen at
ments (refer to Practice C390).
the other mean temperatures listed in Table 1.
10.3 Qualification Requirements—The physical require-
11.4.4 Hot Surface Performance—Test one specimen.
ments shown in Table 1 except density are defined as qualifi-
11.4.5 Water Absorption—Test three specimens as pre-
cationrequirements(refertoPracticeC390).Densityisdefined
scribedinTestMethodC272/C272M,ProcedureAwithsample
as an inspection requirement.
size 12 by 12 by 1 in. (305 by 305 by 25 mm) or Test Method
11. Specimen Selection and Preparation
C1763, Procedure C.
11.4.6 Water Vapor Permeability—Test three specimens as
11.1 Prior to the cutting of any test specimens, a period of at
prescribed in Test Method E96/E96M.
least 72 h shall elapse from the end of primary manufacturing
11.4.7 Dimensional Stability—Test three specimens.
to allow for final polymerization (see 3.4.7 and 3.4.3). The test
11.4.8 Closed Cell Content—Test three specimens.
specimens shall be cut from the buns of material as required by
Annex A1 for the reasons described in Appendix X1.
11.5 Number of specimens to test for each bun tested for
11.2 All test specimens shall be homogeneous per the each required property for box-pour bunstock PIR. Due to the
possible variability from bun to bun within a batch of box-pour
definition of “homogeneous material” in Terminology C168.
bunstock PIR, it is necessary to test three buns from a given
All test specimens shall be free of joints unless the size of the
batch (see A1.3):
specimenrequiredprecludesitbeingcutfromasingle3ftlong
bun. 11.5.1 Density—Test three specimens.
C591 − 22
11.5.2 Compressive Resistance—Test six specimens. 12.5 Water Absorption—Report in units of % by volume
11.5.3 Apparent Thermal Conductivity—Test three speci- determined by multiplying the water absorption % by weight
obtained by testing in accordance with Test Method C272/
mens at mean temperature of 75°F (24°C) and one specimen at
the other mean temperatures listed in Table 1. C272M, Procedure A with sample size 12 by 12 by 1 in. (305
by 305 by 25 mm) or Test Method C1763, Procedure C, by the
11.5.4 Hot Surface Performance—Test one specimen.
specimen specific gravity.
11.5.5 Water Absorption—Test three specimens as pre-
scribedinTestMethodC272/C272M,ProcedureAwithsample
12.6 Water Vapor Permeability—Determine in accordance
size 12 by 12 by 1 in. (305 by 305 by 25 mm) or Test Method
with Test Methods E96/E96M using the desiccant procedure at
C1763, Procedure C.
73 6 2°F (23 6 1°C). See Note 3.
11.5.6 Water Vapor Permeability—Test three specimens as
NOTE 3—The application of a vapor retarder may be required in
prescribed in Test Method E96/E96M.
conjunction with the application of this insulation.
11.5.7 Dimensional Stability—Test three specimens.
11.5.8 Closed Cell Content—Test three specimens.
12.7 Dimensional Stability—Determine in accordance with
Test Method D2126. Exposure time shall be 168 h (one week)
12. Test Methods 62 h. Specimens shall be rectangular prisms with a minimum
size of 4 by 4 by 1 in. (100 by 100 by 25 mm) with the 1 in.
12.1 Density—Determine in accordance with Test Method
(25 mm) dimension being in the rise (height) direction (see
D1622/D1622M or C303.
X1.2.1.1 and X1.3.1.1).
12.2 Com
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C591 − 21 C591 − 22
Standard Specification for
Unfaced Preformed Rigid Cellular Polyisocyanurate Thermal
Insulation
This standard is issued under the fixed designation C591; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This specification covers the types, physical properties, and dimensions of unfaced, preformed rigid cellular polyisocyanurate
plastic material intended for use as thermal insulation on surfaces from –297°F (–183°C) to 300°F (149°C). For specific
applications, the actual temperature limits shall be agreed upon by the manufacturer and purchaser.
1.2 This specification only covers “polyurethane modified polyisocyanurate” thermal insulation which is commonly referred to as
“polyisocyanurate” thermal insulation. This standard does not encompass all polyurethane modified materials. Polyurethane
modified polyisocyanurate and other polyurethane materials are similar, but the materials will perform differently under some
service conditions.
1.3 This standard is designed as a material specification, not a design document. Physical property requirements vary by
application and temperature. At temperatures below –70°F (–51°C) the physical properties of the polyisocyanurate insulation at
the service temperature are of particular importance. Below –70°F (–51°C) the manufacturer and the purchaser must agree on what
additional cold temperature performance properties are required to determine if the material can function adequately for the
particular application.
1.4 This standard addresses requirements of unfaced preformed rigid cellular polyisocyanurate thermal insulation manufactured
using blowing agents with an ozone depletion potential of 0 (ODP 0).
1.5 Except 6.2 and 8.2 – 8.4, which are related to the size and shape of fabricated parts, and 16.1, which is related to the storage
of fabricated parts, the requirements in this standard specification apply to the polyisocyanurate insulation in the form of buns
supplied by the insulation manufacturer.
1.6 When adopted by an authority having jurisdiction, codes that address fire properties in many applications regulate the use of
the thermal insulation materials covered by this specification. Fire properties are controlled by job, project, or other specifications
where codes or government regulations do not apply.
1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
This specification is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.22 on Organic and
Nonhomogeneous Inorganic Thermal Insulations.
Current edition approved April 15, 2021Dec. 1, 2022. Published May 2021December 2022. Originally approved in 1966. Last previous edition approved in 20202021 as
C591 – 20.C591 – 21. DOI: 10.1520/C0591-21.10.1520/C0591-22.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C591 − 22
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C165 Test Method for Measuring Compressive Properties of Thermal Insulations
C168 Terminology Relating to Thermal Insulation
C177 Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the
Guarded-Hot-Plate Apparatus
C272/C272M Test Method for Water Absorption of Core Materials for Sandwich Constructions
C303 Test Method for Dimensions and Density of Preformed Block and Board–Type Thermal Insulation
C335/C335M Test Method for Steady-State Heat Transfer Properties of Pipe Insulation
C390 Practice for Sampling and Acceptance of Thermal Insulation Lots
C411 Test Method for Hot-Surface Performance of High-Temperature Thermal Insulation
C518 Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
C550 Test Method for Measuring Trueness and Squareness of Rigid Block and Board Thermal Insulation
C585 Practice for Inner and Outer Diameters of Thermal Insulation for Nominal Sizes of Pipe and Tubing
C871 Test Methods for Chemical Analysis of Thermal Insulation Materials for Leachable Chloride, Fluoride, Silicate, and
Sodium Ions
C1045 Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
C1058/C1058M Practice for Selecting Temperatures for Evaluating and Reporting Thermal Properties of Thermal Insulation
C1114 Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
C1303/C1303M Test Method for Predicting Long-Term Thermal Resistance of Closed-Cell Foam Insulation
C1363 Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus
C1763 Test Method for Water Absorption by Immersion of Thermal Insulation Materials
D883 Terminology Relating to Plastics
D1621 Test Method for Compressive Properties of Rigid Cellular Plastics
D1622/D1622M Test Method for Apparent Density of Rigid Cellular Plastics
D2126 Test Method for Response of Rigid Cellular Plastics to Thermal and Humid Aging
D2856 Test Method for Open-Cell Content of Rigid Cellular Plastics by the Air Pycnometer (Withdrawn 2006)
D6226 Test Method for Open Cell Content of Rigid Cellular Plastics
E84 Test Method for Surface Burning Characteristics of Building Materials
E96/E96M Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
3. Terminology
3.1 For descriptions of terms used in this specification, refer to Terminologies C168 and D883.
3.2 The term polyisocyanurate does not encompass all polyurethane containing materials (see 1.2).
3.3 The term “core specimen” refers to representative samples cut in accordance with the sampling procedure listed within each
property test method.
3.4 Definitions of Terms Specific to This Standard:
3.4.1 aged, v—in relation to thermal conductivity testing, the act of delaying thermal conductivity testing for a specified time
period after the final polymerization.
3.4.1.1 Discussion—
Unfaced preformed rigid cellular polyisocyanurate thermal insulation samples are aged because the thermal conductivity of this
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
C591 − 22
material increases with time, primarily due to changes in the composition of the gas contained within the closed cells. The rate
of this thermal conductivity increase diminishes with time so an aging time prior to testing is selected to reasonably represent the
long-term performance of the material. The aging time for thermal conductivity test specimens of material covered by this standard
is typically 180 days.
3.4.2 conditioned, v—the act of putting specimens in specified temperature and humidity conditions immediately prior to testing
to allow the specimens to reach temperature and moisture content equilibrium.
3.4.2.1 Discussion—
Samples are conditioned for a fairly short time period (typically 12 to 24 h) during which the test lab holds the sample at standard
lab conditions (see 11.3) immediately prior to testing. If specimens are aged (see 3.4.1) for thermal conductivity testing at the same
conditions specified for conditioning and kept at these conditions until the time of testing, then a separate conditioning period at
the end of the aging period is not necessary.
3.4.3 final polymerization, n—the final chemical reaction and cooling that occurs immediately following primary manufacturing
of unfaced preformed rigid cellular polyisocyanurate thermal insulation materials created using a simultaneous blowing and
exothermic polymerization process.
3.4.3.1 Discussion—
Unfaced preformed rigid cellular polyisocyanurate thermal insulation materials created using a simultaneous blowing and
exothermic polymerization process are formed into a shape such as a bun during manufacture. This shape reaches its final form
and size during primary manufacturing and is at a temperature substantially above ambient. This shape continues to undergo final
polymerization and cooling for a time period ranging from a few hours to several days. This period of final polymerization and
cooling is part of the manufacturing process and samples are not taken for testing or quality control until the end of this period
is reached.
3.4.4 insulation fabricator, n—a company that machines, cuts, grinds, or otherwise transforms the unfaced polyisocyanurate bun
insulation received from an insulation manufacturer into various shapes such as boards, blocks, pipe shells, tank segments, and
elbows/fittings.
3.4.4.1 Discussion—
It is possible for a company to function as both an insulation fabricator and an insulation manufacturer. In this standard
specification the insulation fabricator is also referred to simply as the fabricator.
3.4.5 insulation manufacturer, n—a company engaged in primary manufacturing of unfaced polyisocyanurate foam.
3.4.5.1 Discussion—
It is possible for a company to function as both an insulation manufacturer and an insulation fabricator. In this standard
specification the insulation manufacturer is also referred to simply as the manufacturer.
3.4.6 ozone depletion potential (ODP), n—a relative index indicating the extent to which a chemical product causes ozone
depletion.
3.4.6.1 Discussion—
The reference level of 1 is the potential of trichlorofluoromethane (R-11 or CFC-11) to cause ozone depletion. ODP 0 is an ozone
depletion potential of zero.
3.4.7 primary manufacturing, n—the initial manufacturing step of unfaced preformed rigid cellular polyisocyanurate thermal
insulation materials that begins with the mixing of the precursor chemicals and ends with the formation of the final bun shape.
4. Classification
4.1 Unfaced, preformed rigid cellular polyisocyanurate thermal insulation covered by this specification is classified into six types
as follows:
4.1.1 Type I—Compressive resistance of 20 lb/in (137 kPa), minimum.
4.1.2 Type IV—Compressive resistance of 22 lb/in (150 kPa), minimum.
4.1.3 Type II—Compressive resistance of 35 lb/in (240 kPa), minimum.
4.1.4 Type III—Compressive resistance of 45 lb/in (310 kPa), minimum.
C591 − 22
4.1.5 Type V—Compressive resistance of 80 lb/in (550 kPa), minimum.
4.1.6 Type VI—Compressive resistance of 125 lb/in (862 kPa), minimum.
4.2 Unfaced, preformed rigid cellular polyisocyanurate thermal insulation covered by this specification is classified into one grade
as follows:
4.2.1 Grade 2–Service temperature range of -297°F (-183°C) to 300°F (149°C).
5. Ordering Information
5.1 Orders for materials purchased under this specification shall include the following:
5.1.1 Designation of this specification and year of issue,
5.1.2 Product name or grade/type, or both,
5.1.3 Apparent thermal conductivity and specific thickness required,
5.1.4 Product dimensions,
5.1.5 Quantity of material,
5.1.6 Special packaging or marking, if required, and
5.1.7 Special requirements for inspection or testing, or both.
6. Materials and Manufacture
6.1 Unfaced, preformed rigid cellular polyisocyanurate thermal insulation is produced by the polymerization of polymeric
polyisocyanates in the presence of polyhydroxyl compounds, catalysts, cell stabilizers, and blowing agents.
6.2 The material covered by this specification shall be supplied in “bun” form by the manufacturer. From these buns, a fabricator
shall transform and supply boards, blocks, pipe shells, tank segments, elbows/fittings, or special shapes as agreed upon by the
fabricator and end-user.
7. Physical Properties
7.1 Unfaced, preformed rigid cellular polyisocyanurate thermal insulation shall conform to the requirements shown in Table 1. See
Note 1. For each physical property requirement, the average from testing the number of test specimen(s) required by 11.4 of this
specification shall be used to determine compliance.
NOTE 1—It is the responsibility of the user of this standard to determine the technical requirements for their specific applications and to select an
appropriate Type of material.
7.2 Polyisocyanurate thermal insulation is an organic material and is combustible. Do not expose this insulation to flames or other
ignition sources. The fire performance of the material shall be addressed through fire test requirements established by the
appropriate governing authority. The manufacturer shall be contacted for specific data as fire performance characteristic will vary
with grade, type, and thickness.
7.3 Not all physical properties at temperatures below -70°F (-51°C) have been fully tested. Where these properties are critical, the
user shall consult the manufacturer for properties and performance at these lower temperatures.
C591 − 22
TABLE 1 Physical Property Requirements
A
Grade 2: Operating Temperature Range -297°F (-183°C) to 300°F (149°C)
NOTE 1—Grade 1, which was specific to PIR for use at operating temperatures of -70°F (-51°C) to 300°F (149°C) , was deleted in 2009 because this
material was no longer produced. Grade 2 was not renumbered to minimize conflict with various global engineering and end-user specifications which
require the use of materials complying with, “ASTM C591, Grade 2”.
Property Type I Type IV Type II Type III Type V Type VI
3 3
Density, min lb/ft (kg/m ) 1.8 (29) 2.0 (32) 2.5 (40) 3.0 (48) 4.0 (60) 6.0 (96)
Compressive resistance at 10 % deformation 20 (137) 22 (150) 35 (240) 45 (310) 80 (550) 125 (862)
or yield whichever occurs first, parallel to
rise, min, lb/in (kPa)
Apparent thermal conductivity, max
Btu-in/h-ft -°F (W/m-K),
at a mean temperature of:
-200°F (-129°C) .13 (.019) .13 (.019) .13 (.019) .14 (.020) .14 (.020) .15 (.022)
-150°F (-101°C) .15 (.022) .15 (.022) .15 (.022) .16 (.023) .16 (.023) .17 (.025)
-100°F (-73°C) .17 (.025) .17 (.025) .17 (.025) .18 (.026) .18 (.026) .19 (.027)
-50°F (-46°C) .19 (.027) .19 (.027) .19 (.027) .20 (.029) .20 (.029) .21 (.030)
0°F (-17°C) .19 (.027) .19 (.027) .19 (.027) .20 (.029) .20 (.029) .22 (.032)
50°F (10°C) .18 (.026) .18 (.026) .18 (.026) .19 (.027) .19 (.027) .21 (.030)
75°F (24°C) .19 (.027) .19 (.027) .19 (.027) .20 (.029) .20 (.029) .22 (.032)
150°F (66°C) .23 (.033) .23 (.033) .23 (.033) .24 (.035) .24 (.035) .26 (.037)
200°F (93°C) .26 (.037) .26 (.037) .26 (.037) .27 (.039) .27 (.039) .30 (.044)
Water absorption, max, % by volume 2.0 2.0 1.0 1.0 1.0 0.8
Water vapor permeability, max, perm-in (ng/Pa-s-m) 4.0 (5.8) 4.0 (5.8) 3.5 (5.1) 3.0 (4.4) 2.5 (3.7) 2.0 (2.9)
Dimensional stability, max % linear change, 1 week exposure
158 ± 4°F (70 ± 2°C), 97 + 3 % relative humidity 4 4 4 4 4 4
-40 ± 6°F (-40 ± 3°C), ambient relative humidity 1 1 1 1 1 1
212 ± 4°F (100 ± 2°C), ambient relative humidity 2 2 2 2 2 2
Closed cell content, min 90 90 90 90 90 90
B
Hot-surface performance, at 300°F (149°C) Pass Pass Pass Pass Pass Pass
A
This specification does not purport to address all the performance issues associated with its use. It is the responsibility of the user of this standard to establish appropriate
performance criteria.
B
Pass ⁄fail criteria found in 12.4.
8. Dimensions and Tolerances
8.1 The polyisocyanurate bun dimensions shall be as agreed upon by the purchaser and the manufacturer. Polyisocyanurate buns
are commonly available in lengths up to 144 in. (3.66 m), widths up to 48 in. (1.22 m), and thicknesses from 12 in. (305 mm) to
24 in. (610 mm).
8.2 Insulation Board (cut from buns by a fabricator):
8.2.1 Dimensional tolerances for boards shall be as follows:
Dimension Tolerance, in. (mm)
Length ± ⁄8 (3.2)
Width ± ⁄16 (1.6)
Thickness ± ⁄32 (0.8)
8.2.2 Edge Trueness—Determine in accordance with Test Method C550. The maximum deviation from the edge trueness shall not
be greater than ⁄32 in./ft (2.6 mm/m) of length or width.
8.2.3 Face Trueness—Determine in accordance with Test Method C550. The maximum deviation from flatness shall not be greater
than ⁄16 in./ft (5.2 mm/m) of length or width.
8.2.4 Corner Squareness—Determine in accordance with Test Method C550. The maximum deviation from corner squareness
shall not be greater than ⁄8 in. (3.2 mm) for all board thicknesses.
C591 − 22
8.2.5 Edge Squareness—Determine in accordance with Test Method C550. The maximum deviation from edge squareness shall
not be greater that ⁄16 in. (1.6 mm) for all board thicknesses.
8.3 Pipe Insulation (cut from buns by a fabricator)—Material supplied for pipe insulation shall have dimensions and tolerances
that are in accordance with Practice C585.
8.4 Other parts or special shapes (cut from buns by a fabricator) shall have dimensions and tolerances agreed upon by the
purchaser and fabricator.
9. Workmanship and Appearances
9.1 The polyisocyanurate thermal insulation shall have no defects that will adversely affect its service qualities.
10. Sampling
10.1 Unless otherwise specified, the polyisocyanurate thermal insulation shall be sampled and inspected for acceptance of material
in accordance with Practice C390.
10.2 Inspection Requirements—The requirements for density shown in Table 1, the dimensional requirements described in Section
8, and the workmanship and appearance requirements described in Section 9 are defined as inspection requirements (refer to
Practice C390).
10.3 Qualification Requirements—The physical requirements shown in Table 1 except density are defined as qualification
requirements (refer to Practice C390). Density is defined as an inspection requirement.
11. Specimen Selection and Preparation
11.1 Prior to the cutting of any test specimens, a period of at least 72 h shall elapse from the end of primary manufacturing to
allow for final polymerization (see 3.4.7 and 3.4.3). The test specimens shall be cut from the buns of material as required by Annex
A1 for the reasons described in Appendix X1.
11.2 All test specimens shall be homogeneous per the definition of “homogeneous material” in Terminology C168. All test
specimens shall be free of joints unless the size of the specimen required precludes it being cut from a single 3 ft long bun.
11.3 Unless otherwise specified, the test specimens shall be conditioned (see 3.4.2) at 73 6 4°F (23 6 2°C) and 50 6 5 % relative
humidity for at least 24 h prior to testing.
11.4 Number of specimens to test for each required property for continuous bunstock PIR (see A1.2):
11.4.1 Density—Test three specimens.
11.4.2 Compressive Resistance—Test six specimens.
11.4.3 Apparent Thermal Conductivity—Test three specimens at mean temperature of 75°F (24°C) and one specimen at the other
mean temperatures listed in Table 1.
11.4.4 Hot Surface Performance—Test one specimen.
11.4.5 Water Absorption—Test three specimens as prescribed in Test Method C272/C272M, Procedure A with sample size 12 by
12 by 1 in. (305 by 305 by 25 mm) or Test Method C1763, Procedure C.
11.4.6 Water Vapor Permeability—Test three specimens as prescribed in Test Method E96/E96M.
11.4.7 Dimensional Stability—Test three specimens.
C591 − 22
11.4.8 Closed Cell Content—Test three specimens.
11.5 Number of specimens to test for each bun tested for each required property for box-pour bunstock PIR. Due to the possible
variability from bun to bun within a batch of box-pour bunstock PIR, it is necessary to test three buns from a given batch (see
A1.3):
11.5.1 Density—Test three specimens.
11.5.2 Compressive Resistance—Test six specimens.
11.5.3 Apparent Thermal Conductivity—Test three specimens at mean temperature of 75°F (24°C) and one specimen at the other
mean temperatures listed in Table 1.
11.5.4 Hot Surface Performance—Test one specimen.
11.5.5 Water Absorption—Test three specimens as prescribed in Test Method C272/C272M, Procedure A with sample size 12 by
12 by 1 in. (305 by 305 by 25 mm) or Test Method C1763, Procedure C.
11.5.6 Water Vapor Permeability—Test three specimens as prescribed in Test Method E96/E96M.
11.5.7 Dimensional Stability—Test three specimens.
11.5.8 Closed Cell Content—Test three specimens.
12. Test Methods
12.1 Density—Determine in accordance with Test Method D1622/D1622M or C303.
12.2 Compressive Resistance—Determine in accordance with Test Method C165, Procedure A or Test Method D1621, at a
crosshead speed of 0.1 in/min (2.5 mm/min) for each 1 in. (25 mm) of specimen thickness. See Note 2.
NOTE 2—Polyisocyanurate insulation can be anisotropic and, therefore, strength properties can vary with direction. The manufacturer should be consulted
if additional information is required.
12.3 Apparent Thermal Conductivity—Determine in accordance with Test Method C177, C518, C1114 or C1363 in accordance
with Practice C1045 using the small temperature differences indicated in Practice C1058/C1058M, Table 3 with the specimen cut
so that the induced direction of heat flow is parallel to the rise (height) direction of the bun. In some cases where this insulation
is used in pipe applications, Test Method C335/C335M is applicable. Core 1 in. (25 mm) thick test specimens shall be cut from
buns after the final polymerization (see 3.4.3 and 11.1) is complete, be aged (3.4.1) at 73 6 4°F (23 6 2°C) and 50 6 5 % relative
humidity for 180 6 5 days from time of specimen cutting, be conditioned if necessary (see 3.4.2), and then tested following these
aging (and conditioning if
...