5.1 The purpose of this test method is to provide a means for comparing relative water absorption tendencies between different cellular plastics. It is intended for use in specifications, product evaluation, and quality control. It is applicable to specific end-use design requirements only to the extent that the end-use conditions are similar to the immersion period (normally 96 h) and 5.1-cm [2-in.] head requirements of the test method.

5.2 This test method provides a means for measuring absorption as a result of direct contact exposure to free water. Results by this test method cannot be used to compare the resistance of cellular plastics to water vapor transmission and subsequent condensation within the cells. To determine resistance to water vapor transmission, see Test Methods E96 .

5.3 Water absorption testing is subject to several important variables, which if not considered, prohibit sufficient agreement among testing laboratories. Development of this test method has taken into account the most serious of the possible sources of error.

5.4 The volume error associated with surface cells opened during specimen preparation decreases as the cell size decreases. This test method provides the option to ignore this variable with cellular plastics that have an average cell diameter of 0.03 cm or less. For cellular plastics having greater than 0.03-cm average cell diameter and in all cases of dispute, measurement of cell size shall be mandatory in determining the specimen volume.

5.5 For most materials the size of the test specimens is small compared with the size of the products actually installed in the field. If the surface-to-volume ratios for the test specimens and the corresponding products are different, it is possible that the test results are misleading.

5.6 In most cases water retention is a secondary performance characteristic that has an influence on a primary characteristic, such as thermal performance, surface accumulation of moisture, localized collection of electrolytes, dimensional stability, etc.

5.7 Before proceeding with this test method, reference shall be made to the specification of the material being tested. Any test specimen preparation, conditioning, dimensions, or testing parameters covered in the materials specification, or both, shall take precedence over those mentioned in this test method. If there are no material specifications, then the default conditions in this standard shall apply.

1.1 This test method covers the determination of the water absorption of rigid cellular plastics by measuring the change in buoyant force resulting from immersion under a 5.1-cm (2-in.) head of water for the specified immersion period of 96 h.

1.2 This test method describes two procedures that shall be used to measure the change in buoyant force. Procedure A shall be used for materials that either experience rapid water absorption or that show an increase in volume during the exposure period, or both. Materials that do not exhibit either of these characteristics shall be evaluated by Procedure B.

1.3 For specific applications, immersion periods varying from the normal 96-h test requirement shall be agreed upon between the manufacturer and the purchaser.

1.4 The values stated in SI units are to be regarded as the standard.