Nafio (R) impregnated Solupor (R), microporous UHMWPE film, (N-PE), Nafion (R) 117 (N117) and a membrane prepared using a DE2020 Nafion (R) dispersion (DE2020) were characterized with respect to their swelling degree (SD), methanol cross-over, proton conductivity and DMFC performance at various methanol concentrations in order to understand the effect of impregnation of an ion-conductive polymer membrane to the fuel cell performance. Introducing Nafion (R) into the pores of Solupor (R) causes reduction of both methanol cross-over and proton conductivity. Low proton conductivity of the N-PE membrane is compensated by its significantly low methanol cross-over and this leads to better DMFC performance at 1 and 6 M concentrations in comparison to N117 and DE2020 membranes. In addition to that, N-PE composite membrane has high dimensional stability, low membrane thickness, good performance using less Naflon (R) ionomer, with reduced cost. In addition to the real fuel cell measurements, characteristic P values of the membranes were also calculated using both thickness dependent and independent methods. All characteristic values failed to predict the real fuel cell performance and should be used with caution. (C) 2008 Elsevier B.V. All rights reserved.