5.1 The purpose of these tests is to obtain, by means of simple apparatus, reliable values for water vapor transfer rate through materials, expressed in suitable units.

5.2 A WVTR value obtained in one method under one set of test conditions is not necessarily indicative of the value that would be obtained using the other method or under a different set of conditions. See Appendix X3 for discussion of determining dependency of WVTR on different relative humidity (at a given temperature).

5.3 Commonly used test conditions are listed in Appendix X1, but given the above caution, the selection of test conditions other than those listed, and which closely approach exposure conditions of material in actual use, is allowed. Where tests are conducted for classification or compliance purposes, environmental conditions are typically defined in product standard specifications.

1.1 These test methods cover the determination of water vapor transmission rate (WVTR) of materials, such as, but not limited to, paper, plastic films, other sheet materials, coatings, foams, fiberboards, gypsum and plaster products, wood products, and plastics. Two basic methods, the Desiccant Method and the Water Method, are provided for the measurement of WVTR. In these tests, the desired temperature and side-to-side humidity conditions, with resultant vapor drive through the specimen, are used. The test conditions employed are at the discretion of the user, but in all cases, are reported with the results.

1.2 The values stated in either Inch-Pound or SI units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, each system shall be used independently of the other. Derived results are converted from one system to the other using appropriate conversion factors (see Table 1).

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.