Direct methanol fuel cells require membranes with the dual properties of high proton conductivity and low methanol crossover. Such membranes have a high selectivity, that is a high ratio of proton conductivity to methanol permeability. This research reports such a membrane made of polyvinylalcohol and loaded with mordenite, a proton conducting, methanol impermeable zeolite. Protons travel directly through both the polymer and zeolite phases, but methanol has a more tortuous path around the zeolite particles. The composite membranes show up to twenty times higher selectivity than Nafion, the current benchmark. The improved behavior, a result of the proper tailoring of the polymer and dispersion phase, is predicted using Maxwell's theory for diffusion in composite media.