Despite the use of a standard test method, variations in experimental conditions make comparison of permeation results difficult. Studies which quantify the effect of several variables on chemical permeation and its measurement were conducted in order to improve the interpretation of permeation test results. The variables studied included temperature, material thickness, experimental setup (cell size, open versus closed loop), and detector sensitivity. Both theoretical and experimental approaches were taken. Fickian diffusion principles were used to characterize permeation mathematically and model the effect of the above variables. Permeation experiments were conducted for several material/chemical combinations using different-sized permeation cells and several cell temperatures. Also, permeation through several thicknesses of fluorinated ethylene-propylene [FEP (Teflon)] was measured. The 2.5-cm-diameter (1-in.) ASTM-type cell provided greater precision than the standard 5-cm (2-in.) cell, but with longer breakthrough times. Breakthrough times were seen to be profoundly affected by temperature, material thickness, and detector sensitivity.