Following the growing interest from year to year in synthesizing composite materials used for drug release, this paper proposes a theoretical investigation in order to contribute to the development of a mathematical model able to describe the process mentioned above. The majority of the models presented in literature are empirical, more or less complex. We propose here a theoretical mathematical model, based on physical phenomena such as diffusion in porous media in unsteady state. The simplifying assumptions of the model concerning the geometry and the morphology of the composite materials will be presented and discussed.