Test method ASTM D2221 is referenced by ASTM D3575. It is used to determine the compression creep properties of package cushioning materials. That is, the test determines the extent and nature of the change in thickness of a cushion under a given long-term static load. In practice, that change in thickness might occur during the storage, handling, or shipment of the cushioned product. Data obtained by this test method apply to a cushion only under the conditions of the test, however, and may not be a measure of the actual creep that would occur in a completed package.