Permeability (P) and diffusion (D) coefficients of perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene copolymers were determined with respect to different gases (He, H-2, O-2, N-2, CO2, hydrocarbons C-1-C-3). The copolymers with large content of perfluorodioxole comonomer exhibit high permeability with respect to lighter gases comparable to that of poly(trimethylsilyl propyne). However, the copolymers studied are much more permselective than the latter polymer. Free volume as estimated via Bondi’s method and free volume size distribution parameters which were determined by means of positron annihilation lifetimes (PAL) method are also unusually high if compared with other glassy polymers. A novel correlation of the P and D values, as well as of the solubility coefficients S with the PAL parameter tau(4)I(4) are reported.