The permeability and diffusivity of oxygen, carbon dioxide, nitrogen, and helium have been obtained for a range of linear low density polyethylene (LLDPE) films prepared from the same raw materials but with different processing conditions. The measurements were carried out by means of a permeation technique over the temperature interval where the ␣-relaxation processes were observed in earlier studies. The temperature dependence of the permeability and diffusion coefficients of gases shows 2 well-differentiated regions in all films. The break temperature of these regions is approximately located at the same temperature as the ␣-relaxation takes place. Both the permeability and their temperature dependence do not show a noticeable influence on the processing conditions. The effect of processing conditions on the diffusivity seems to be more complex. Differences are observed for different films in the diffusion coefficients, in the case of oxygen, and in their change with the temperature, which is particularly marked in the case of carbon dioxide. Fujita's free volume model has been applied to diffusivity data in order to study the influence of films microstructure in gas permeation properties through them.