Composite polymer proton exchange membranes (PEM) were prepared by solution recasting. The composite membranes formed are based on Nafion incorporating a silane functionalized zeolite, mordenite, as an additive. The composite membranes were placed within a single cell DMFC and compared to an MEA featuring a standard Nation 125 mu m membrane. The impact of mordenite particle size, the choice of the silane functionalizing agent and the membrane preparation procedure are investigated. A composite ion exchange membrane which featured Nation and a ground mordenite which was functionalized using glycidoxypropyltrimethoxysilane achieved a power density that outperformed a standard Nation MEA under all conditions. (C) 2010 Elsevier B.V. All rights reserved.