AbstractA series of gas permeability studies of plastic membranes demonstrated the strong dependence of gas transport on structural aspects of the membrane. Films of cellulose acetate butyrate, silicone rubber, polyethylene, polypropylene, and vinyl chloride, were used in these studies. The effect of elastic and nonelastic stretching, orientation, plasticization, and phase changes were shown to be detectable by gas permeations. Interpretation of the permeation response, as a function of temperature, is compatible with a thermodynamic appraisal of the permeation process.