Crosslinked sulfonated triblock copolymers exhibit lower methanol permeability and good physical strength relative to the perfluorinated proton conductive membranes typically used in Direct Methanol Fuel Cells. Examples of triblock copolymers that can be used as fuel cell membranes include SEBS, SIBS, and SEPS. The chemically cross-linked and sulfonated SIBS, SEBS, and SEPS exhibit lower swelling and tolerate higher sulfonation levels than the un-cross-linked counterparts. These copolymers are easily sulfonated using known procedures and can be manufactured at a fraction of the cost of the typical perfluorinated proton conductive membranes.