Polymer membranes are disclosed having increased permeability. The process of the present disclosure, for instance, can increase the ion permeability of membranes and/or the gas permeability of membranes. In one embodiment, for instance, a precursor polymer is subjected to energy in an amount sufficient to form damage tracks through the thickness of the polymer. The damage tracks are then oxidized to form free radical groups. The precursor polymer is then hydrolyzed causing ion groups to form that cluster along the damage tracks. In one embodiment, sulfonated tetrafluoroethylene-based copolymer ionomer membranes are formed that have increased conductivity. Other ionomer membranes that may be formed according to the present disclosure include copolymers of a vinyl hydrocarbon and a vinyl carboxylic acid.