Radiation-induced graft copolymerization of hydroxyethyl methacrylate with hydroxyethyl acrylate, acrylic acid or glycidyl methacrylate on ethylene tetrafluoroethylene (ETFE) films allow for tailor-made synthesis of membranes for high and low temperature fuel cell applications. According to the operating temperatures proton conductivity may be achieved via doping with phosphoric acid or a two-step sulfonation of the functional monomers. Fuel cell tests provide power densities and internal resistances, which indicate that the membranes are suitable for high and low temperature fuel cells.