Permeation of three hydrogen isotopes, methane, and inert gases were measured for a tetrafluoroethylene (TFE) and a polyethylene (PE) film at room temperature by means of the time‐lag method in order to establish physicochemical properties which determine the solubility and the diffusivity of these gases. It was observed that the diffusion constant of the inert gases changed exponentially with the heat of vaporization, and their solubility constant was an exponential function of the Lennard‐Jones force constant of the gases for both films. On the other hand, hydrogen isotopes and methane deviated from these relations. It is concluded that the dispersive force plays an important role for the solution and the diffusion of the inert gases, whereas chemical interactions between the solute and the solvent play an important role.