Currently available polymeric roofing membranes are ordinarily evaluated in a battery of tests that are hopefully indicators of in-situ performance. Field performance of some products has suggested that dimensional stability may be important among these. The test for such a property (ASTM D-1204) is a hot air bath environment for measured membrane samples. Presently, test environments are selected by manufacturers and range widely in the market. To promote congruency in testing/reporting, a scale is proposed for future testing within categories defined by generic polymer type.