ASTM C870-24

Standard Practice for Conditioning of Thermal Insulating Materials

SIGNIFICANCE AND USE
5.1 The conditioning prescribed in this recommended practice is designed to obtain reproducible test results on thermal insulating materials. Results of tests obtained on these materials under uncontrolled atmospheric conditions are not comparable with each other. Some of the physical properties of thermal insulating materials are influenced by relative humidity and temperature in a manner that affects the results of tests. In this regard, such information is provided in pertinent material specifications and test methods by stating the physical properties relative to the specific ambient or test conditions.
Note 1: In some cases (for example, dimensionally unstable materials), the dry mass cannot easily be established and original mass has to be used.
SCOPE
1.1 This practice covers the conditioning of thermal insulating materials for tests. Since prior exposure of insulating materials to high or low humidity will affect the equilibrium moisture content, a procedure is also given for preconditioning the materials.  
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.3 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.  
1.4 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: 29-Feb-2024
• ICS: 91.100.60 - Thermal and sound insulating materials
• Technical Committee: C16 - Thermal Insulation
• Drafting Committee: C16.31 - Chemical and Physical Properties

Relations

• Replaces: ASTM C870-11(2017) - Standard Practice for Conditioning of Thermal Insulating Materials
• Effective Date: 01-Mar-2024
• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM C168-22 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 01-May-2022
• Referred By: ASTM C302-13(2022) - Standard Test Method for Density and Dimensions of Preformed Pipe-Covering-Type Thermal Insulation
• Effective Date: 01-Mar-2024
• Referred By: ASTM C1763-20 - Standard Test Method for Water Absorption by Immersion of Thermal Insulation Materials
• Effective Date: 01-Mar-2024
• Referred By: ASTM C1774-13(2019) - Standard Guide for Thermal Performance Testing of Cryogenic Insulation Systems
• Effective Date: 01-Mar-2024
• Referred By: ASTM C533-17(2023) - Standard Specification for Calcium Silicate Block and Pipe Thermal Insulation
• Effective Date: 01-Mar-2024
• Referred By: ASTM C335/C335M-23 - Standard Test Method for Steady-State Heat Transfer Properties of Pipe Insulation
• Effective Date: 01-Mar-2024
• Referred By: ASTM C303-21 - Standard Test Method for Dimensions and Density of Preformed Block and Board–Type Thermal Insulation
• Effective Date: 01-Mar-2024
• Referred By: ASTM C203-22 - Standard Test Methods for Breaking Load and Flexural Properties of Block-Type Thermal Insulation
• Effective Date: 01-Mar-2024
• Referred By: 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
• Referred By: ASTM C209-20 - Standard Test Methods for Cellulosic Fiber Insulating Board
• Effective Date: 01-Mar-2024
• Referred By: ASTM C764-19 - Standard Specification for Mineral Fiber Loose-Fill Thermal Insulation
• Effective Date: 01-Mar-2024
• Referred By: ASTM C1512-10(2020) - Standard Test Method for Characterizing the Effect of Exposure to Environmental Cycling on Thermal Performance of Insulation Products
• Effective Date: 01-Mar-2024
• Referred By: ASTM C578-23 - Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation
• Effective Date: 01-Mar-2024

Overview

ASTM C870-24: Standard Practice for Conditioning of Thermal Insulating Materials provides a systematic procedure for conditioning thermal insulation materials before testing. By standardizing preconditioning and conditioning methods, this practice ensures that test results are reproducible and comparable, regardless of laboratory or environmental variations. The standard addresses the critical influence of relative humidity and temperature on the physical properties of thermal insulating materials, which can impact material performance data if not properly controlled.

Effective conditioning of insulating materials eliminates differences that arise from exposure to uncontrolled atmospheric conditions, thereby enhancing accuracy and repeatability in testing. This practice is widely referenced in material specifications and test methods for thermal insulation, supporting enhanced quality control and regulatory compliance across the industry.

Key Topics

• Conditioning and Preconditioning Procedures: The standard outlines specific steps for bringing insulation materials to equilibrium moisture content. Preconditioning is essential if the material has experienced variable humidity exposure, ensuring consistency prior to conditioning and testing.
• Moisture Content and Equilibrium: Definitions such as moisture content, moisture regain, and equilibrium moisture conditions are clarified to ensure consistent interpretation and application.
• Atmospheric Control: Detailed instructions for maintaining standard testing atmospheres (humidity and temperature) using conditioning rooms or chambers.
• Instrumentation and Measurement: Recommendations for instruments, such as balances with high sensitivity and devices for monitoring humidity and temperature, to support precise conditioning procedures.
• Repeatable Test Results: The practice is designed specifically to enable interlaboratory and intralaboratory comparability by eliminating environmental factors that could skew physical property data.
• Safety and Compliance: Users are reminded to implement appropriate safety, health, and environmental practices and to ensure adherence to relevant regulations.

Applications

• Thermal Insulation Material Testing: This standard is fundamental for laboratories, manufacturers, and quality-control professionals who need consistent, reproducible results when testing the physical properties of insulation products.
• Product Development and Certification: Conditioning prescribed by ASTM C870-24 is applicable to R&D, helping developers ensure that prototypes and new products meet strict industry requirements and performance expectations.
• Quality Assurance in Manufacturing: By conditioning samples to specified moisture and temperature equilibria, manufacturers can verify product consistency, optimize performance characteristics, and reduce batch-to-batch variability.
• Regulatory and Specification Compliance: Many construction and industrial standards require that insulation products be tested according to precisely defined conditioning protocols. Compliance with ASTM C870-24 ensures that thermal insulating materials meet both domestic and international standards.
• Interlaboratory Testing Programs: When cross-laboratory comparisons or certifications are necessary, standardized conditioning eliminates discrepancies due to atmospheric differences, ensuring trust in comparative data.

Related Standards

• ASTM C168 - Terminology Relating to Thermal Insulation
• ASTM E171 - Practice for Conditioning and Testing Flexible Barrier Packaging
• ASTM E337 - Test Method for Measuring Humidity with a Psychrometer
• ISO 139 - Standard Atmospheres for Conditioning and Testing
• Material-Specific Specifications - Refer to individual insulation product standards for properties affected by conditioning

Keywords: ASTM C870, conditioning, preconditioning, thermal insulation, moisture equilibrium, test methods, humidity control, insulation material testing, reproducibility, quality assurance.

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: C870 − 24
Standard Practice for
Conditioning of Thermal Insulating Materials
This standard is issued under the fixed designation C870; 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.
1. Scope E337 Test Method for Measuring Humidity with a Psy-
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
1.1 This practice covers the conditioning of thermal insu-
peratures)
lating materials for tests. Since prior exposure of insulating
2.2 ISO Standard:
materials to high or low humidity will affect the equilibrium
ISO 139 Standard atmospheres for conditioning and testing
moisture content, a procedure is also given for preconditioning
the materials.
3. Terminology
1.2 The values stated in either SI units or inch-pound units
3.1 Definitions—Definitions of terms in the field of thermal
are to be regarded separately as standard. The values stated in
insulating materials are given in Terminology C168. The
each system may not be exact equivalents; therefore, each
following definitions are derived from Terminology E41:
system shall be used independently of the other. Combining
3.1.1 moisture content—the moisture present in a material,
values from the two systems may result in non-conformance
as determined by definite prescribed methods, expressed as a
with the standard.
percentage of the mass of the sample on either of the following
1.3 This standard does not purport to address all of the
bases: (1) original mass (see 3.1.1); (2) moisture-free weight
safety concerns, if any, associated with its use. It is the
(see 3.1.2).
responsibility of the user of this standard to establish appro-
3.1.1.1 Discussion—This is variously referred to as mois-
priate safety, health, and environmental practices and deter-
ture content, or moisture “as is” or “as received.”
mine the applicability of regulatory limitations prior to use.
3.1.1.2 Discussion—This is also referred to as moisture
1.4 This international standard was developed in accor-
regain (frequently contracted to “regain”), or moisture content
dance with internationally recognized principles on standard-
on the “oven-dry,” “moisture-free,” or “dry” basis.
ization established in the Decision on Principles for the
3.1.2 moisture equilibrium—the condition reached by a
Development of International Standards, Guides and Recom-
sample when the net difference between the amount of mois-
mendations issued by the World Trade Organization Technical
ture sorbed and the amount desorbed, as shown by a change in
Barriers to Trade (TBT) Committee.
mass, shows no trend and becomes insignificant.
3.1.2.1 Discussion—Superficial equilibrium with the film of
2. Referenced Documents
air in contact with the specimen is reached very rapidly. Stable
2.1 ASTM Standards:
equilibrium can be reached in a reasonable time only if the air
C168 Terminology Relating to Thermal Insulation
to which the sample is exposed is in motion. Stable equilibrium
E41 Terminology Relating to Conditioning (Withdrawn
with air in motion is considered to be realized when successive
2019)
weighings do not show a progressive change in mass greater
E171 Practice for Conditioning and Testing Flexible Barrier
than the tolerances established for the various insulating
Packaging
materials.
3.1.3 moisture regain—the moisture in a material deter-
mined under prescribed conditions, and expressed as a percent-
This practice is under the jurisdiction of ASTM Committee C16 on Thermal
age of the mass of the moisture-free specimen.
Insulation and is the direct responsibility of Subcommittee C16.31 on Chemical and
3.1.3.1 Discussion—Moisture regain calculations are com-
Physical Properties.
monly based on the mass of a specimen that has been dried by
Current edition approved March 1, 2024. Published March 2024. Originally
approved in 1977. Last previous edition approved in 2017 as C870 – 11 (2017). heating in an oven. If the air in the oven contains moisture, the
DOI: 10.1520/C0870-24.
oven-dried specimen will contain some moisture even when it
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
no longer shows a significant change in mass. In order to
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.
3 4
The last approved version of this historical standard is referenced on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
www.astm.org. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C870 − 24
ensure that the specimen is moisture-free, it must be exposed to 3.2.5 See Appendix X1 – Appendix X3 for related nonman-
desiccated air until it shows no further significant change in its datory information.
mass. For drying temperatures above 100°C [212°F], the
4. Summary of Practice
moisture content of the oven atmosphere is negligible.
3.1.3.2 Discussion—Moisture regain may be calculated 4.1 Specimens are brought to a low moisture content in the
from moisture content using Eq 1, and moisture content may be
preconditioning atmosphere, and subsequently brought to con-
calculated from moisture regain using Eq 2 as follows: ditioned moisture equilibrium in the conditioning atmosphere
in accordance with the specified test method.
C
R 5 × 100 (1)
100 2 C
5. Significance and Use
R
C 5 × 100 (2)
5.1 The conditioning prescribed in this recommended prac-
1001R
tice is designed to obtain reproducible test results on thermal
where:
insulating materials. Results of tests obtained on these materi-
C = moisture content, % (see 3.1.1), and als under uncontrolled atmospheric conditions are not compa-
R = moisture regain, % (see 3.1.3).
rable with each other. Some of the physical properties of
thermal insulating materials are influenced by relative humidity
3.2 Definitions of Terms Specific to This Standard—The
and temperature in a manner that affects the results of tests. In
following descriptions apply only to the usage of terms in this
this regard, such information is provided in pertinent material
practice:
specifications and test methods by stating the physical proper-
3.2.1 preconditioned moisture equilibrium—The moisture
ties relative to the specific ambient or test conditions.
condition reached by a sample or specimen after exposure to
NOTE 1—In some cases (for example, dimensionally unstable
moving air at the standard atmosphere for preconditioning. The
materials), the dry mass cannot easily be established and original mass has
final condition may be established after a specified period of
to be used.
time, or at a moisture equilibrium that is considered to have
been reached when the change in mass of a specimen in
6. Apparatus
successive weighings made at intervals of not less than 2 h
6.1 Conditioning Room or Chamber:
does not exceed 0.2 % of the mass of the specimen.
6.1.1 Equipment for maintaining the standard atmosphere
3.2.2 conditioned moisture equilibrium—The moisture con-
for testing insulating materials throughout the room or chamber
dition reached by a sample or specimen during free exposure to
within the tolerance given in 3.2.4, and including facilities for
moving air controlled at specified conditions. For test purposes,
circulating the air
...

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: C870 − 11 (Reapproved 2017) C870 − 24
Standard Practice for
Conditioning of Thermal Insulating Materials
This standard is issued under the fixed designation C870; 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.
1. Scope
1.1 This practice covers the conditioning of thermal insulating materials for tests. Since prior exposure of insulating materials to
high or low humidity will affect the equilibrium moisture content, a procedure is also given for preconditioning the materials.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.3 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 and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.4 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:
C168 Terminology Relating to Thermal Insulation
E41 Terminology Relating to Conditioning (Withdrawn 2019)
E171 Practice for Conditioning and Testing Flexible Barrier Packaging
E337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
2.2 ISO Standard:
ISO 544ISO 139 Standard Atmospheres for Conditioning and/or Testingatmospheres for conditioning and testing
3. Terminology
3.1 Definitions—Definitions of terms in the field of thermal insulating materials are given in Terminology C168. The following
definitions are derived from Terminology E41:
3.1.1 moisture content—the moisture present in a material, as determined by definite prescribed methods, expressed as a
percentage of the mass of the sample on either of the following bases: (1) original mass (see 3.1.1); (2) moisture-free weight (see
3.1.2).
This practice is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.31 on Chemical and Physical
Properties.
Current edition approved April 15, 2017March 1, 2024. Published May 2017March 2024. Originally approved in 1977. Last previous edition approved in 20112017 as
C870 – 11.C870 – 11 (2017). DOI: 10.1520/C0870-11R17.10.1520/C0870-24.
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.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C870 − 24
3.1.1.1 Discussion—
This is variously referred to as moisture content, or moisture “as is” or “as received.”
3.1.1.2 Discussion—
This is also referred to as moisture regain (frequently contracted to “regain”), or moisture content on the “oven-dry,”
“moisture-free,” or “dry” basis.
3.1.2 moisture equilibrium—the condition reached by a sample when the net difference between the amount of moisture sorbed
and the amount desorbed, as shown by a change in mass, shows no trend and becomes insignificant.
3.1.2.1 Discussion—
Superficial equilibrium with the film of air in contact with the specimen is reached very rapidly. Stable equilibrium can be reached
in a reasonable time only if the air to which the sample is exposed is in motion. Stable equilibrium with air in motion is considered
to be realized when successive weighings do not show a progressive change in mass greater than the tolerances established for the
various insulating materials.
3.1.3 moisture regain—the moisture in a material determined under prescribed conditions, and expressed as a percentage of the
mass of the moisture-free specimen.
3.1.3.1 Discussion—
Moisture regain calculations are commonly based on the mass of a specimen that has been dried by heating in an oven. If the air
in the oven contains moisture, the oven-dried specimen will contain some moisture even when it no longer shows a significant
change in mass. In order to ensure that the specimen is moisture-free, it must be exposed to desiccated air until it shows no further
significant change in its mass. For drying temperatures above 100°C [212°F], the moisture content of the oven atmosphere is
negligible.
3.1.3.2 Discussion—
Moisture regain may be calculated from moisture content using Eq 1, and moisture content may be calculated from moisture regain
using Eq 2 as follows:
C
R 5 ×100 (1)
100 2 C
R
C 5 ×100 (2)
1001R
where:
C = moisture content, % (see 3.1.1), and
R = moisture regain, % (see 3.1.3).
3.2 Definitions of Terms Specific to This Standard—The following descriptions apply only to the usage of terms in this practice:
3.2.1 preconditioned moisture equilibrium—The moisture condition reached by a sample or specimen after exposure to moving
air at the standard atmosphere for preconditioning. The final condition may be established after a specified period of time, or at
a moisture equilibrium that is considered to have been reached when the change in mass of a specimen in successive weighings
made at intervals of not less than 2 h does not exceed 0.2 % of the mass of the specimen.
3.2.2 conditioned moisture equilibrium—The moisture condition reached by a sample or specimen during free exposure to moving
air controlled at specified conditions. For test purposes, moisture equilibrium must be reached by absorption, starting from a
relatively low moisture content (see 3.2.3). Moisture equilibrium for testing is considered to have been reached when the rate of
increase in the mass of a sample or specimen does not exceed that specified for the material being tested. In the absence of a
specified rate, an increase of less than 0.1 % of the sample mass after a 24-h exposure is considered satisfactory.
3.2.2.1 Discussion—
Because the standard preconditioning atmosphere covers a range of relative humidities, the close approach to equilibrium is, in
general, warranted only at the top of the range. At lower humidities exposure for several hours is usually sufficient.
3.2.3 standard preconditioning atmosphere—An atmosphere having uncontrolled humidity and a constant temperature within the
range from 100 to 120°C [212 to 248°F], or a specified lower temperature if these temperatures would be destructive to the
specimens. Refer to material specification.
3.2.4 standard conditioning atmosphere—Air maintained at a relative humidity of 50 6 5 % and at a temperature of 23 6 2°C
[73 6 4°F]. This atmosphere may be used for testing without preconditioning specimens if it has been determined that the property
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