AbstractNew data are reported for the permeation of inert gases through polyethylene, polytetrafluoroethylene, and silicone and natural rubbers. Additional data are compiled from the literature. The relative solubilities of these gases are practically insensitive to chemical variations in the homopolymer. Hence variations in structure at the glass transition (Tg) and melting (Tm) temperatures that affect diffusion also unambiguously affect permcation. Consequently an equivalence results between permeation at a given temperature for different polymers and permeation at different temperatures for a given polymer. Although the diffusion coefficient changes continuously with temperature, the Arrhenius parametersDoandEdapparently change discontinuously atTgandTm. Their magnitudes and variations with atomic weight reach maxima at aboutTg. These data indicate a dependence of the classical correlation betweenDoandEdon polymer properties. A perturbed diameter for the permeant, specific for each polymer, is proposed for correlating theDoandEddata. This correlation makes the changes observed atTgandTmmore perceptible.