The main purpose of the study was to assess the usability of a new calculation technique for determining the relationship between effective moisture diffusivity and moisture concentration. Four types of autoclaved aerated concrete, differing in their densities, were chosen as model porous media. The drying curves and the moisture distribution for samples that had different drying times were determined experimentally. The results obtained were used in a numerical procedure to give an estimation of the diffusion coefficient. The dependence of the coefficient on the moisture concentration was approximated by a polygonal chain. An entirely satisfactory correlation with experimental data was obtained by the application of an eight-segment polygonal chain. It was found that the diffusion coefficient was a decreasing function with respect to the moisture concentration in the low moisture content range. It reached a minimum and then increased together with the moisture concentration. It was also concluded that the greater the density of the tested porous material the lower its effective diffusivity. (C) 2018 Elsevier Ltd. All rights reserved.