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The accurate estimation of the thermal performance of insulation products over their expected lifetime has been a recognized challenge for over twenty years. This is because the lifetime of such products is long (10-25 years), thermal aging is caused by the diffusion of a multitude of gases, and the insulation product is not homogeneous. Two classical approaches to accelerating diffusion controlled phenomena, namely aging at higher temperature and aging a thin slice, have limitations when applied to insulation materials like polyisocyanurate (PIR) laminate board. Raising temperature does not change the diffusion coefficients of all the different gases involved in the aging process at the same rate. In the case of pentane blown PIR board, these gases are CO2, air and the different pentane isomers used to blow the foam. Thin slicing of core foam and scaling techniques, such as those in the ASTM C 1303 -00 procedure, do not account for the fact that PIR laminate boards are denser at the surface layer than in the core foam.