4.1 Conditioning of specimens is typically conducted: (1) for the purpose of bringing the material into equilibrium with normal or average room conditions, (2) simply to obtain reproducible results, regardless of previous history of exposure, or (3) to subject the material to abnormal conditions of temperature or humidity in order to predict its service behavior.

4.2 The conditioning procedures prescribed in this practice are designed to obtain reproducible results and have the potential to give physical values somewhat higher or somewhat lower than values under equilibrium at normal conditions, depending upon the particular material and test. Depending on the thickness, type of material and its previous history, it is possible that it would take 20 to 100 days or more to ensure substantial equilibrium under normal conditions of humidity and temperature. Consequently, conditioning for reproducibility must of necessity be used for general purchase specifications and product control tests.

1.1 In general, the physical and electrical properties of plastics are influenced by temperature and relative humidity in a manner that materially affects test results. In order to make reliable comparisons between different materials and between different laboratories, it is necessary to standardize the humidity conditions, as well as the temperature, to which specimens of these materials are subjected prior to and during testing. This practice defines procedures for conditioning plastics (although not necessarily to equilibrium) prior to testing, and the conditions under which they shall be tested.

1.2 For some materials, it is possible that a material specification exists that requires the use of this practice, but with some procedural modifications. The material specification takes precedence over this practice. Refer to the material specification before using this practice. Table 1 in Classification D4000 lists the ASTM material specifications that currently exist.

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.

Note 1: This standard and ISO 291 address the same subject matter, but differ in technical content. ISO 291 describes only two temperature and humidity conditions for conditioning or testing, or both.

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.