ASTM F1249-20

Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor

SIGNIFICANCE AND USE
5.1 The purpose of this test method is to obtain reliable values for the WVTR of plastic film and sheeting.  
5.2 WVTR is an important property of packaging materials and can often be directly related to shelf life and packaged product stability.  
5.3 Data from this test method is suitable as a referee method of testing, provided that the purchaser and seller have agreed on sampling procedures, standardization procedures, test conditions, and acceptance criteria.
SCOPE
1.1 This test method covers a procedure for determining the rate of water vapor transmission through flexible barrier materials. The method is applicable to sheets and films up to 3 mm (0.1 in.) in thickness, consisting of single or multilayer synthetic or natural polymers and foils, including coated materials. It provides for the determination of (1) water vapor transmission rate (WVTR), (2) the permeance of the film to water vapor, and (3) for homogeneous materials, water vapor permeability coefficient.  
Note 1: Values for water vapor permeance and water vapor permeability must be used with caution. The inverse relationship of WVTR to thickness and the direct relationship of WVTR to the partial pressure differential of water vapor may not always apply.  
1.2 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.  
1.3 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: 31-May-2020
• ICS: 83.140.10 - Films and sheets
• Technical Committee: F02 - Primary Barrier Packaging
• Drafting Committee: F02.10 - Permeation

Relations

• Replaces: ASTM F1249-13 - Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor
• Effective Date: 01-Jun-2020
• 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 E96/E96M-23 - Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials
• Effective Date: 15-Nov-2023
• Refers: ASTM E178-16 - Standard Practice for Dealing With Outlying Observations
• Effective Date: 01-Jun-2016
• Refers: ASTM E96/E96M-15 - Standard Test Methods for Water Vapor Transmission of Materials
• Effective Date: 01-May-2015
• Refers: ASTM E96/E96M-14 - Standard Test Methods for Water Vapor Transmission of Materials
• Effective Date: 15-Oct-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E96/E96M-13 - Standard Test Methods for Water Vapor Transmission of Materials
• Effective Date: 01-Nov-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E96/E96M-12 - Standard Test Methods for Water Vapor Transmission of Materials
• Effective Date: 15-Dec-2012
• Refers: ASTM E104-02(2012) - Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions
• Effective Date: 01-Apr-2012
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM E96/E96M-10 - Standard Test Methods for Water Vapor Transmission of Materials
• Effective Date: 01-Oct-2010
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010

Overview

ASTM F1249-20, titled "Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor", is a widely recognized testing standard developed by ASTM International. This method establishes procedures for determining the Water Vapor Transmission Rate (WVTR), as well as water vapor permeance and permeability, of flexible barrier materials such as plastic films, polymer sheets, foils, and coated materials. With applications up to 3 mm in thickness, ASTM F1249-20 plays a key role in material selection and product development for packaging and related industries.

Key Topics

• Water Vapor Transmission Rate (WVTR):

  • Measures the rate at which water vapor permeates through plastic film or sheeting.
  • Reported as the amount of water vapor passing through a defined area over a specified time under controlled conditions.

• Modulated Infrared Sensor Technology:

  • The method employs a diffusion cell separated by the test specimen, with a dry chamber and a wet chamber.
  • Water vapor that permeates the barrier material is detected and quantitatively measured by a modulated infrared sensor.
  • Sensor output is proportional to the concentration of water vapor and used to calculate WVTR accurately.

• Permeance and Permeability:

  • Permeance: Ratio of WVTR to vapor pressure difference; significant for comparing different materials under varying conditions.
  • Permeability Coefficient: Relevant for homogeneous materials and incorporates both permeance and material thickness.

• Testing Considerations:

  • Applicable to single and multilayer synthetic or natural polymers and foils.
  • Requires careful control of temperature, humidity, and sample preparation to ensure repeatable and reproducible results.
  • Calibration of test equipment with reference films is essential for accuracy.

Applications

• Packaging Materials Validation:
  Ensures that plastic films and barrier sheets used in food, pharmaceutical, medical, and industrial packaging limit moisture ingress or egress as required for product stability and longer shelf life.

• Product Development:
  Provides quantitative data for selecting suitable materials or evaluating new barrier technologies during R&D.

• Quality Control:
  Used by manufacturers and converters of plastic films to control product consistency and compliance with customer or regulatory specifications.

• Dispute Resolution:
  The method is recognized as a referee standard when purchaser and seller need agreed, validated data for material acceptance or rejection.

• Regulatory Compliance:
  Supports documentation for compliance with international requirements for packaging performance, especially for moisture-sensitive goods.

Related Standards

• ASTM E96/E96M - Test Methods for Water Vapor Transmission of Materials:
  Covers gravimetric measurement of water vapor transmission and is often referenced for other material types.

• ASTM D374 - Test Methods for Thickness of Solid Electrical Insulation:
  Provides procedures for measuring the thickness of materials, which is a critical factor in WVTR assessment.

• ASTM E104 - Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions:
  Specifies procedures to control humidity environments during WVTR testing.

• ASTM E177, E178, E691 - Practices related to precision, bias, outlier handling, and interlaboratory testing.

Practical Value

Implementing ASTM F1249-20 allows organizations to validate the moisture barrier performance of plastic films and sheeting with confidence, supporting product reliability and regulatory acceptance. It forms a foundation for industry best practices in material testing, facilitating global trade and competitive product development through standardized, repeatable, and transparent test results. The use of a modulated infrared sensor ensures sensitive and accurate measurement suited to a broad range of barrier materials in modern packaging and related industries.

Keywords: Water vapor transmission rate, WVTR, permeability, permeance, plastic film, sheeting, packaging barriers, ASTM F1249, modulated infrared sensor, flexible barrier materials, moisture barrier, packaging standard, material testing.

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: F1249 − 20
Standard Test Method for
Water Vapor Transmission Rate Through Plastic Film and
Sheeting Using a Modulated Infrared Sensor
This standard is issued under the fixed designation F1249; 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 E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
1.1 This test method covers a procedure for determining the
E178 Practice for Dealing With Outlying Observations
rate of water vapor transmission through flexible barrier
E691 Practice for Conducting an Interlaboratory Study to
materials. The method is applicable to sheets and films up to 3
Determine the Precision of a Test Method
mm (0.1 in.) in thickness, consisting of single or multilayer
synthetic or natural polymers and foils, including coated
3. Terminology
materials. It provides for the determination of (1) water vapor
3.1 Definitions:
transmission rate (WVTR), (2) the permeance of the film to
3.1.1 water vapor permeability coeffıcient—the product of
water vapor, and (3) for homogeneous materials, water vapor
the permeance and the thickness of the film. The permeability
permeability coefficient.
is meaningful only for homogeneous materials, in which case
NOTE 1—Values for water vapor permeance and water vapor perme-
it is a property characteristic of bulk material.
ability must be used with caution. The inverse relationship of WVTR to
3.1.1.1 Discussion—This quantity should not be used unless
thickness and the direct relationship of WVTR to the partial pressure
the relationship between thickness and permeance has been
differential of water vapor may not always apply.
verified in tests using several thicknesses of the material. An
1.2 This standard does not purport to address all of the
accepted unit of permeability is the metric perm centimeter, or
safety concerns, if any, associated with its use. It is the
2 2
(g·cm)/(m ·day·mmHg).TheSIunitisthe(mol·mm)/(m ·s·Pa).
responsibility of the user of this standard to establish appro-
The test conditions must be stated.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use. 3.1.2 water vapor permeance—the ratio of a barrier’s
1.3 This international standard was developed in accor- WVTR to the vapor pressure difference between the two
dance with internationally recognized principles on standard-
surfaces.
ization established in the Decision on Principles for the 3.1.2.1 Discussion—An accepted unit of permeance is the
Development of International Standards, Guides and Recom-
metric perm, or g/(m ·day·mmHg). The SI unit is the mol/
mendations issued by the World Trade Organization Technical (m ·s·Pa). Since the permeance of a specimen is generally a
Barriers to Trade (TBT) Committee.
function of relative humidity and temperature, the test condi-
tions must be stated.
2. Referenced Documents
3.1.3 water vapor transmission rate (WVTR)—the time rate
2.1 ASTM Standards: of water vapor flow normal to the surfaces, under steady-state
E96/E96M Test Methods for Water Vapor Transmission of conditions, per unit area.
Materials 3.1.3.1 Discussion—An accepted unit of WVTR is
E104 Practice for Maintaining Constant Relative Humidity g/(m ·day). The test conditions of relative humidity and tem-
by Means of Aqueous Solutions perature where the humidity is the difference in relative
humidity across the specimens, must be stated.
4. Summary of Test Method
This test method is under the jurisdiction ofASTM Committee F02 on Primary
Barrier Packaging and is the direct responsibility of Subcommittee F02.10 on
4.1 A dry chamber is separated from a wet chamber of
Permeation.
known temperature and humidity by the barrier material to be
CurrenteditionapprovedJune1,2020.PublishedJuly2020.Originallyapproved
tested. The dry chamber and the wet chamber make up a
in 1989. Last previous edition approved in 2013 as F1249 – 13. DOI: 10.1520/
F1249-20.
diffusion cell in which the test film is sealed. Water vapor
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
diffusing through the film mixes with the gas in the dry
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
chamberandiscarriedtoapressure-modulatedinfraredsensor.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. This sensor measures the fraction of infrared energy absorbed
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1249 − 20
FIG. 2 Conditioning System
FIG. 1 Measuring System
6.1.1.2 Diffusion Cell Sealing Surface—A flat rim around
the dry side of the diffusion cell. This is a critical sealing
by the water vapor and produces an electrical signal, the
surface against which the test specimen is pressed; it shall be
amplitude of which is proportional to water vapor concentra-
smooth and without radial scratches.
tion.The amplitude of the electrical signal produced by the test
6.1.1.3 Diffusion Cell Air Passages—Two holes in the dry
film is then compared to the signal produced by measurement
half of the diffusion cell. This is necessary only in the earlier
of a calibration film of known water vapor transmission rate.
model WVTR instruments that have a separate conditioning
This information is then used to calculate the rate at which
rack and testing chamber. These shall incorporate O–rings
moisture is transmitted through the material being tested.
suitable for sealing the diffusion cell to the test chamber
pneumatic fittings for the introduction and exhaust of air
5. Significance and Use
without significant loss or leakage.
5.1 The purpose of this test method is to obtain reliable
NOTE 2—Use of Multiple Diffusion Cells—Experience has shown that
values for the WVTR of plastic film and sheeting.
arrangements using multiple diffusion cells are a practical way to increase
the number of measurements that can be obtained in a given time. A
5.2 WVTR is an important property of packaging materials
separate conditioning rack (Fig. 2) may be used to start the permeation
and can often be directly related to shelf life and packaged
process, prior to analyzing on an instrument.Aconditioning rack contains
product stability.
a manifold which connects the dry-chamber side of each individual
diffusion cell to a dry-air source. Dry air is continually purging the dry
5.3 Data from this test method is suitable as a referee
chamber of those cells that are connected to the conditioning rack while
method of testing, provided that the purchaser and seller have
the humid chamber side is held at a specific relative humidity by distilled
agreed on sampling procedures, standardization procedures,
water or a saturated-salt solution. It is desirable to thermostatically control
test conditions, and acceptance criteria. the temperature of the conditioning rack as described in 6.1.3.
6.1.2 Test Chamber—A cavity into which the diffusion cell
6. Apparatus
is inserted. Again, this is necessary only in the earlier model
WVTR instruments that have a separate conditioning rack and
6.1 This method utilizes water vapor transmission apparatus
(Fig. 1) comprised of the following: testing chamber. The test chamber shall incorporate means for
6.1.1 Diffusion Cell—An assembly consisting of two metal clamping the diffusion cell in accurate registration with pneu-
halves which, when closed upon the test specimen, will matic system openings to the dry-air source and the infrared
accurately define a circular area.Atypical acceptable diffusion detector. The chamber shall also provide a thermometer well
cell area is 50 cm . The volume enclosed by each cell half, for the measurement of temperature.
when clamped, is not critical; it should be small enough to 6.1.3 Diffusion Cell Temperature Control—It is desirable to
allow for rapid gas exchange, but not so small that an thermostatically control the temperature of the diffusion cell to
unsupported film that happens to sag or buckle will contact the within 60.6°C.Asimple resistive heater attached to the station
top or bottom of the cell. A depth of approximately 6 mm in such a manner as to ensure good thermal contact is adequate
(0.250 in.) has been found to be satisfactory for 50-cm cells. forthispurpose.Athermistorsensorandanappropriatecontrol
6.1.1.1 Diffusion Cell O–Ring—An appropriately sized circuit will serve to regulate the temperature unless measure-
groove machined into the humid chamber side of the diffusion ments are being made close to ambient temperature. In that
cellretainsaneopreneO–ring.Thetestareaisconsideredtobe case it may be necessary to provide cooling coils to remove
the area established by the inside contact diameter of the some of the heat.
compressed O–ring when the diffusion cell is clamped shut 6.1.4 Flowmeter—Ameansforregulatingtheflowofdryair
against the test specimen. within an operating range of 5 to 100 cc/min is required.
F1249 − 20
6.1.5 Flow-Switching Valves, for the switching of dry-gas
flow streams of the water vapor transmission apparatus.
6.1.6 Infrared Sensor—A water vapor detector capable of
sensing 1 µg/L of water, or, in other terms, 1 ppm by volume,
or 0.002 % relative humidity at 37.8°C.
6.1.7 Recording Device—A multirange strip chart recorder
or other appropriate instrument for measuring the voltage
developed by the signal amplifier.
6.1.8 Desiccant Drying System, shall be capable of reducing
the concentration of water vapor in the gas source down to less
than 0.5 ppm by volume or 0.001 % relative humidity at
37.8°C. In earlier model WVTR equipment, a separate desic-
FIG. 3 Film Diffusion Cell
cant drying system is needed for the conditioning rack and test
chamber.
6.1.9 Flow-Metering Valve—A fine-metering valve capable
10.3 Preparation of Test Samples:
of controlling the dry-gas flow rate to the test cell when the
10.3.1 Cut the test specimen to approximately 10 cm by 10
apparatus is in the “measure” mode of operation.
cm (4 in. by 4 in.).
10.3.2 If required, measure specimen thickness at four
7. Reagents and Materials
equally spaced points within the test area and at the center.
7.1 Desiccant, for drying gas stream.
Note: if a sample is fragile (such as a thin coating or
unprotected metallization) the act of measuring the material
7.2 Absorbent Pads (not critical), such as filter pads of 30 to
might compromise or scratch the barrier layer. For such
75 mm in diameter. Necessary only in earlier model WVTR
samples, analyzing the material thicknessAFTER transmission
equipment that utilizes distilled water or saturated salt solu-
rate testing may be preferable.
tions to generate the desired relative humidity.
10.3.3 Lightly grease the cell sealing surface and the cell
7.3 Distilled Water, for producing 100 % relative humidity,
O–ring.
or various saturated salt solutions to produce other relative
10.3.4 ForearliermodelWVTRsystemsthatrequiretheuse
humidities as described in Practice E104. Newer WVTR
of distilled water or saturated salt solutions, insert one to three
equipment does not require saturated salt solutions. Refer to
absorbent pads into the lower half-cell and dampen with
the manufacturer’s instructions for generating relative humid-
distilled wate
...

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: F1249 − 13 F1249 − 20
Standard Test Method for
Water Vapor Transmission Rate Through Plastic Film and
Sheeting Using a Modulated Infrared Sensor
This standard is issued under the fixed designation F1249; 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 test method covers a procedure for determining the rate of water vapor transmission through flexible barrier materials.
The method is applicable to sheets and films up to 3 mm (0.1 in.) in thickness, consisting of single or multilayer synthetic or natural
polymers and foils, including coated materials. It provides for the determination of (1) water vapor transmission rate (WVTR), (2)
the permeance of the film to water vapor, and (3) for homogeneous materials, water vapor permeability coefficient.
NOTE 1—Values for water vapor permeance and water vapor permeability must be used with caution. The inverse relationship of WVTR to thickness
and the direct relationship of WVTR to the partial pressure differential of water vapor may not always apply.
1.2 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.3 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:
D374 Test Methods for Thickness of Solid Electrical Insulation (Metric) D0374_D0374M
D1898 Practice for Sampling of Plastics (Withdrawn 1998)
E96/E96M Test Methods for Water Vapor Transmission of Materials
E104 Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E178 Practice for Dealing With Outlying Observations
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions:
3.1.1 water vapor permeability coeffıcient—the product of the permeance and the thickness of the film. The permeability is
meaningful only for homogeneous materials, in which case it is a property characteristic of bulk material.
This test method is under the jurisdiction of ASTM Committee F02 on FlexiblePrimary Barrier Packaging and is the direct responsibility of Subcommittee F02.10 on
Permeation.
Current edition approved Oct. 1, 2013June 1, 2020. Published November 2013July 2020. Originally approved in 1989. Last previous edition approved in 20112013 as
F1249 – 06 (2011).F1249 – 13. DOI: 10.1520/F1249-13.10.1520/F1249-20.
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.
3.1.1.1 Discussion—
This quantity should not be used unless the relationship between thickness and permeance has been verified in tests using several
thicknesses of the material. An accepted unit of permeability is the metric perm centimeter, or 1 g/m(g·cm)/(m per day per mm
Hg·cm of thickness. ·day·mmHg). The SI unit is the mol/m(mol·mm)/(m ·s·Pa·mm.·s·Pa). The test conditions (see 3.1) must be
stated.
3.1.2 water vapor permeance—the ratio of a barrier’s WVTR to the vapor pressure difference between the two surfaces.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1249 − 20
3.1.2.1 Discussion—
An accepted unit of permeance is the metric perm, or 1 g/mg/(m per day per mm Hg. ·day·mmHg). The SI unit is the
mol/mmol/(m ·s·Pa.·s·Pa). Since the permeance of a specimen is generally a function of relative humidity and temperature, the test
conditions must be stated.
3.1.3 water vapor transmission rate (WVTR)—the time rate of water vapor flow normal to the surfaces, under steady-state
conditions, per unit area.
3.1.3.1 Discussion—
FIG. 1 Measuring System
An accepted unit of WVTR is g/mg/(m per day. ·day). The test conditions of relative humidity and temperature where the humidity
is the difference in relative humidity across the specimens, must be stated.
4. Summary of Test Method
4.1 A dry chamber is separated from a wet chamber of known temperature and humidity by the barrier material to be tested.
The dry chamber and the wet chamber make up a diffusion cell in which the test film is sealed. Water vapor diffusing through the
film mixes with the gas in the dry chamber and is carried to a pressure-modulated infrared sensor. This sensor measures the fraction
of infrared energy absorbed by the water vapor and produces an electrical signal, the amplitude of which is proportional to water
vapor concentration. The amplitude of the electrical signal produced by the test film is then compared to the signal produced by
measurement of a calibration film of known water vapor transmission rate. This information is then used to calculate the rate at
which moisture is transmitted through the material being tested.
5. Significance and Use
5.1 The purpose of this test method is to obtain reliable values for the WVTR of plastic film and sheeting.
5.2 WVTR is an important property of packaging materials and can often be directly related to shelf life and packaged product
stability.
5.3 Data from this test method is suitable as a referee method of testing, provided that the purchaser and seller have agreed on
sampling procedures, standardization procedures, test conditions, and acceptance criteria.
6. Apparatus
6.1 This method utilizes water vapor transmission apparatus (Fig. 1) comprised of the following:
6.1.1 Diffusion Cell—An assembly consisting of two metal halves which, when closed upon the test specimen, will accurately
define a circular area. A typical acceptable diffusion cell area is 50 cm . The volume enclosed by each cell half, when clamped,
is not critical; it should be small enough to allow for rapid gas exchange, but not so small that an unsupported film that happens
to sag or buckle will contact the top or bottom of the cell. A depth of approximately 6 mm (0.250 in.) has been found to be
satisfactory for 50-cm cells.
F1249 − 20
FIG. 2 Conditioning System
6.1.1.1 Diffusion Cell O–Ring —O–Ring—An appropriately sized groove machined into the humid chamber side of the diffusion
cell retains a neoprene O–ring. The test area is considered to be the area established by the inside contact diameter of the
compressed O–ring when the diffusion cell is clamped shut against the test specimen.
6.1.1.2 Diffusion Cell Sealing Surface—A flat rim around the dry side of the diffusion cell. This is a critical sealing surface
against which the test specimen is pressed; it shall be smooth and without radial scratches.
6.1.1.3 Diffusion Cell Air Passages—Two holes in the dry half of the diffusion cell. This is necessary only in the earlier model
WVTR instruments that have a separate conditioning rack and testing chamber. These shall incorporate O–rings suitable for sealing
the diffusion cell to the test chamber pneumatic fittings for the introduction and exhaust of air without significant loss or leakage.
NOTE 2—Use of Multiple Diffusion Cells—Experience has shown that arrangements using multiple diffusion cells are a practical way to increase the
number of measurements that can be obtained in a given time. A separate conditioning rack (Fig. 2) may be used that to start the permeation process,
prior to analyzing on an instrument. A conditioning rack contains a manifold which connects the dry-chamber side of each individual diffusion cell to
a dry-air source. Dry air is continually purging the dry chamber of those cells that are connected to the conditioning rack while the humid chamber side
is held at a specific relative humidity by distilled water or a saturated-salt solution. It is desirable to thermostatically control the temperature of the
conditioning rack as described in 6.1.3.
6.1.2 Test Chamber—A cavity into which the diffusion cell is inserted. Again, this is necessary only in the earlier model WVTR
instruments that have a separate conditioning rack and testing chamber. The test chamber shall incorporate means for clamping
the diffusion cell in accurate registration with pneumatic system openings to the dry-air source and the infrared detector. The
chamber shall also provide a thermometer well for the measurement of temperature.
6.1.3 Diffusion Cell Temperature Control—It is desirable to thermostatically control the temperature of the diffusion cell to
within 61°F.60.6°C. A simple resistive heater attached to the station in such a manner as to ensure good thermal contact is
adequate for this purpose. A thermistor sensor and an appropriate control circuit will serve to regulate the temperature unless
measurements are being made close to ambient temperature. In that case it may be necessary to provide cooling coils to remove
some of the heat.
6.1.4 Flowmeter—A means for regulating the flow of dry air within an operating range of 5 to 100 cc/min is required.
6.1.5 Flow-Switching Valves, for the switching of dry-gas flow streams of the water vapor transmission apparatus.
6.1.6 Infrared Sensor—A water vapor detector capable of sensing 1 μg/L of water, or, in other terms, 1 ppm by volume, or
0.002 % relative humidity at 37.8°C.
6.1.7 Recording Device—A multirange strip chart recorder or other appropriate instrument for measuring the voltage developed
by the signal amplifier.
6.1.8 Desiccant Drying System, shall be capable of reducing the concentration of water vapor in the gas source down to less
than 0.5 ppm by volume or 0.001 % relative humidity at 37.8°C. In earlier model WVTR equipment, a separate desiccant drying
system is needed for the conditioning rack and test chamber.
6.1.9 Flow-Metering Valve—A fine-metering valve capable of controlling the dry-gas flow rate to the test cell when the
apparatus is in the “measure’’“measure” mode of operation.
7. Reagents and Materials
,
7.1 Desiccant, for drying gas stream.
7.2 Absorbent Pads (not critical), such as filter pads of 30 to 75 mm in diameter. Necessary only in earlier model WVTR
equipment that utilizes distilled water or saturated salt solutions to generate the desired relative humidity.
F1249 − 20
FIG. 3 Film Diffusion Cell
7.3 Distilled Water, for producing 100 % relative humidity, or various saturated salt solutions to produce other relative
humidities as described in Practice E104. Newer WVTR equipment does not require saturated salt solutions. Refer to the
manufacturer’s instructions for generating relative humidity.
7.4 Reference Film, known WVTR material for system calibration.
7.5 Sealing Grease, a high-viscosity, silicone stopcock grease or other suitable high-vacuum grease is required for lubrication
of O–rings and to seal the specimen film in the diffusion cell.
7.6 Nitrogen Gas, shall be dry and contain not less than 99.5 % nitrogen. Needed only with certain WVTR instruments.
8. Sampling
8.1 Select material and quantity for testing in accordance with standard methods of sampling applicable to the material under
test. Sampling may be done in accordance with Practice D1898. Select samples considered representative of the material to be
tested. If the material is of nonsymmetrical construction, the orientation should be noted.
9. System Calibration With Reference Film
9.1 Follow the manufacturer’s instructions for calibrating the WVTR instrument with a reference film.
10. Test Procedure
10.1 Preparation of Apparatus (Fig. 1)—If preceding tests have exposed the apparatus to high moisture levels, outgas
...