A kinetic model is proposed to describe the diffusion and adsorption behavior of gas in multilayer films. Numerical solutions are attained on time scales of seconds using a finite differencing approximation to the kinetic equations. Predictions of this model are compared to experimental data for the case of NO2 diffusing through a porphyrin film. The model predicts a binding energy for the NO2 porphyrin interaction of 0.72 eV. It also predicts that for this system diffusion is the limiting factor for the adsorption response time of the film, although the recovery time is determined by both the diffusion coefficient and NO2 binding energy. Comparison with experiment gives a predicted diffusion coefficient of similar to 10(-14) m(2)center dot s(-1).