5.1 The purpose of these tests is to determine water vapor transmission rate of materials by means of a simple gravimetric procedure.

5.2 Test Conditions: 

5.2.1 A WVTR result obtained in one method under one set of test conditions cannot be used to predict the result that would be obtained using the same method with a different set of conditions, or using the other method. See Appendix X3 for discussion of determining dependency of WVTR on different relative humidity (at a given temperature).

5.2.2 Test conditions that are commonly used or are considered standard in various industries or research applications are listed as Procedures A-E in Appendix X1, but use of these conditions is not mandatory in the methods herein.

5.2.3 Given the caution in 5.2.1, the selection of test conditions that closely approach exposure conditions of material in actual use is advised when possible.

5.2.4 Where tests are conducted for classification or compliance purposes, test conditions are typically defined in codes, specifications, and manufacturer’s technical literature.

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.