1. SCOPE 1.1 This procedure defines the long-term thermal resistance (LTTR) of a foam product as the value measured after 5-year storage in a laboratory environment and provides means for its prediction based on an accelerated laboratory test. 1.2 This procedure, based on ASTM standard test methods C 1303 and C 518, can be applied to a wide range of preformed as well as field applied insulating foams. This procedure estimates the change in the thermal resistivity of insulating foam products by means of slicing and scaling. 1.3 This procedure is applicable to products with either permeable or semi-permeable facers which meet the criteria outlined in Clause 7.2 and Clause 7.3 1.4 This test procedure is applicable to cellular plastic insulation manufactured with the intent to retain a blowing agent, other than air, for a period longer than 180 days. This procedure specifies reference time, sampling and testing requirements for the application of ASTM standard test method C 1303 to determine LTTR for closed-cell foams such as extruded polystyrene, sprayed polyurethane, and polyisocyanurate. 1.5 This procedure does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.