This paper addresses the modelling of hygric material coefficients bridging the gap between measured material properties and the non-linear storage and transport coefficients in the transfer equation. The conductivity approach and a bundle of tubes model are the basis. By extending this model with a mechanistic treatment of serial and parallel structured transport, a semi-empirical material model is developed. Deriving the transport properties from the pore structure of the material, the model provides a physical basis whereas a high flexibility and adjustability is obtained by the coupling with the mechanistic model. The required minimum input data are basic standard material properties. The model is very suitable for sophisticated research as well as for a broad application to porous materials in general. (C) 2009 Elsevier Ltd. All rights reserved.