ASTM C1258-21a

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Designation: C1258 − 21 C1258 − 21a
Standard Test Method for
Elevated Temperature and Humidity Resistance of Vapor
Retarders for Insulation
This standard is issued under the fixed designation C1258; 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 the determination of the resistance of flexible low permeance vapor retarders for thermal insulation
as classified in Specification C1136 to elevated temperature and humidity. Water vapor permeance measurement and visual
inspection after exposure at elevated temperature and humidity are used to assess vapor retarder response.
1.2 Typical vapor retarders evaluated in this test method are intended for indoor use and include foil-scrim-kraft laminates,
metallized polyester-scrim-kraft laminates, treated fabrics, treated papers, films, foils, or combinations of these materials that
comprise a vapor retarder material. This test method is not intended for assessment of the liquid-applied coatings, sealants, or
mastics commonly used with insulation products.
1.3 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.
1.4 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.
1.5 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
C1136 Specification for Flexible, Low Permeance Vapor Retarders for Thermal Insulation
E96/E96M Test Methods for Water Vapor Transmission of Materials
3. Terminology
3.1 Terminology C168 shall be considered as applying to the terms used in this specification.
This test method is under the jurisdiction of ASTM Committee C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.33 on Insulation Finishes
and Moisture.
Current edition approved March 1, 2021Sept. 1, 2021. Published April 2021September 2021. Originally approved in 1994. Last previous edition approved in 20192021
as C1258 – 19.C1258 – 21. DOI: 10.1520/C1258-21.10.1520/C1258-21A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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C1258 − 21a
4. Summary of Test Method
4.1 The vapor retarders are exposed to elevated temperature and humidity at 120°F (49°C) and 95 % relative humidity for a period
of 28 days, then visually inspected for corrosion (if applicable), delamination, and other degradation. Water vapor permeance in
accordance with Test Methods E96/E96M is measured after elevated temperature and humidity exposure.
5. Significance and Use
5.1 On systems operating at sub-ambient temperature, humid ambient conditions cause a vapor driving force toward the insulation.
If not retarded, the driven moisture vapor is detrimental to the insulation’s thermal resistance. A vapor retarder must resist
degradation in order maintain its resistance to vapor passage. Degradation in this test method is induced by elevated temperature
and humidity conditions.
6. Apparatus
6.1 Environmental Chamber, capable of maintaining an average of 120 6 2°F (49 6 1°C) and 95 6 2 % relative humidity, using
distilled or deionized water as the humidity source. The chamber shall be of the air-circulating variety.
6.2 Lighted Box, with five opaque sides and one transparent glass or plastic viewing side, illuminated with an incandescent
lightbulb. The viewing area shall be slightly smaller than the vapor retarder specimen so that holes or degradation caused by the
testing conditions are readily visible.
6.3 Darkroom.
6.4 Cotton Gloves.
6.5 Frame/holder of non-reacting material.
6.6 Support of non-reacting material from which to suspend specimens.
6.7 Other mounting accessories of non-reacting material as needed.
7. Test Specimens
7.1 From each sample cut four specimens that are large enou
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