The widespread use of polymer composite materials makes it necessary to study their physical properties. Particular attention is given to polymers reacted with water and other low molecular weight compounds in their preparation as well as during operation. Most studies have been devoted in the diffusion properties of materials in the form of films, while operating materials often have a different shape, for example pellets. Well at small sizes of granules is impossible to use stationary methods. In this paper, the diffusion coefficient is determined by the zonal method based on the integration of the diffusion equation. A significant increase in the effective diffusion coefficient with an increase in the diffusant concentration associated with the plasticizing action of water was detected. Temperature-humidity dependence of diffusion effective coefficient is approximated by the refined formula which helps to calculate mass transfer process kinetics and carry out theoretical analysis of water diffuse properties in polymer matrix. With the movement of individual particles of polymer materials in real dryers, it is expedient to break the kinetic problem of mass transfer into external and internal one. The validity of the two-level consideration of the kinetic problem of granular polymer materials deep drying and the applicability of the data obtained for their diffusion properties are shown. The microkinetics of a single particle drying is considered, it is the determining condition for the accuracy of the kinetic calculation.