Sorption, diffusion and permeability coefficients of argon, hydrogen, propane, propylene and propyne were determined for unfilled poly(dimethylsiloxane) (PDMS) membranes at 308 K and for PDMS membrane filled with palladium nanoclusters (5 wt.%). Time-lag and sorption methods were used to obtain kinetic and equilibrium relevant parameters for characterizing the mass transport. Mass transport in a PDMS composite membrane differs from the corresponding unfilled membrane mainly during the transient regime, when a concentration profile is being settling down across the membrane thickness. The presence of the palladium nanoclusters, modifies the mass transport during the transient regime not only because the nanoclusters can act as adsorption wells (mainly in the case of hydrogen), but also because they lead to a tortuosity increase. At steady-state condition the relevant parameters that characterize the transport are the sorption and diffusion coefficients in the polymeric matrix, the filler volume content and the tortuosity. All experiments were successfully modelled using parameters obtained from independent experiments. (c) 2006 Elsevier B.V. All rights reserved.