A mathematical model able to predict the water transport properties of casein-based edible coating is presented. The model consists of two parts. The first is aimed to describe the water solubilization process into the investigated film, and it was derived taking into account the presence of both "bound water" and "free water". The second is intended to describe the water diffusion process, and it was derived considering both the dependence of water diffusion coefficient of local water concentration and the superposition of polymer relaxation to stochastic diffusion. To validate the model both water sorption isotherm and sorption kinetics of the investigated film were determined at 25 degreesC. The proposed model was successfully fitted to both sorption and diffusion data, corroborating the validity of the hypothesis used to derive it. (C) 2003 Elsevier Science Ltd. All rights reserved.