The permeabilities and diffusivities of dichloromethane, nitroethane and tetrachloroethylene in poly(hexafluoropropylene-co-tetrafluoroethylene), Teflon® FEP, have been determined in a continuous-flow permeation cell over the range 20-100°C. Linear Arrhenius plots of the permeabilities and diffusivities were obtained, with the permeabilities, but not the diffusivities, showing a change of slope at the glass transition temperature, T g. Linear correlations were found between the activation energy for diffusion, E D , and the van der Waals diameter of the diffusant, d, plotted either as d or d 2, and between E D and the logarithm of the pre-exponential parameter for diffusion, ln D 0 . p]The solubility of the permeants calculated from these measurements compares reasonably well with that determined gravimetrically below T g at 30°C. However, application of the dual-mode sorption theory to the gravimetric sorption isotherms shows that sorption by the Langmuir mode at this temperature only makes a small contribution to the greater solubility exhibited by the polymer in the glassy state.