We describe a process of diffusion of low-molecular substance in inhomogeneous heterogeneous polymeric media and composites. A general approximate model for the diffusion process in such materials is proposed. A model represents a two-phase media, one phase of which makes diffusion impossible, and another one makes it possible. Diffusion passes through two channels simulated by two cylindrical rods (pipes), whose axes are chaotically bent in space. Particularly, it is shown that for such media, the Fick solution proposed for a homogeneous media with representative volume element in the form of a rod with diffusing substance applied at the face at the initial instant, cannot be used. An analytic solution, which describes the diffusion process in time and space in accounting for the media heterogeneity, is proposed.