AbstractThe transport of oxygen through oriented PET at 25 and 60°C has been studied using the dynamic diffusion method. It did not prove possible to determine the diffusion and solubility coefficients with reasonable accuracy, and only the permeability coefficients are discussed in terms of the structure of the samples. The results suggest that the lowering of the oxygen permeability on drawing is related to the production of additional material with thetransconformation of the glycol residue, either in crystallites or in amorphous regions, rather than solely to the overall development of orientation or crystallinity