Method and apparatus are provided for accurately and more rapidly measuring the permeability of various test gases in cellular polymeric materials with very low permeation rates, comprising a constant volume test chamber sealed with indium gaskets, said chamber being connected to a gas inlet valve and test gas reservoir with pressure gauge, gas outlet valve and oil check valve, an absolute pressure transducer to track the change in pressure in the test chamber, and said chamber being submerged in a water bath for strict temperature control. A thinly cut foam sample is placed in the test chamber surrounded by the test gas, where the gas inside the sample is first allowed to reach equilibrium with the surrounding gas; the pressure of the surrounding gas is then raised or lowered, and the rate at which the sample takes up or gives off the test gas is recorded over time as a change in pressure of the test gas around the foam. From this pressure variation the desired permeability coefficient may be measured, and achieved more quickly due to the reduced thickness of the sample. Unlike standard prior art transmission-method devices, this new sorption method and apparatus also allows for separate determination of the diffusion and solubility coefficients; it further allows for the use of much thinner foam samples than can be reliably used in prior art methods, resulting in a substantial reduction in testing time. The effective diffusion coefficient is used as an input to a computational model which predicts the rate of aging in a foam insulation panel. The effective solubility coefficient is used primarily to understand the behavior of the blowing agent in the foam system.