This work reports on new method for description of sorption and swelling phenomena in liquid + polymer systems. An innovative approach to description of polymer-solvent interactions combines swelling and sorption properties of polymeric membranes in liquid media. It stems from gravimetric (material mass change) and dilatometric (material volume change) experiments. Further, we introduced a new parameter, a product of the dilatation interaction factor and the solubility of the organic liquid in the swollen polymer, which can describe the "moving ability" of polymer chains of swollen polymer. The approach was developed on the basis of the data determined for low density semicrystalline polyethylene (LDPE) with benzene and cyclohexane derivates. The obtained results are presented as functions of temperature, number of C-atoms in the side chain of liquid cyclic molecules, and as a function of van der Waals volume of liquid penetrants. The moving ability of polymer chains increases with increasing temperature, but decreases with increasing number of C-atoms in the side chain of penetrants. The new parameter was determined also for rubbery polydimethylsiloxane (PDMS), Lukopren, modified Lukopren with embedded montmorillonite and on polyvinylidene fluoride (PVDF) membrane samples. (C) 2017 Elsevier B.V. All rights reserved.