Abstract: A process for making a cation exchange membranes includes impregnating a film of highly fluorinated sulfonic acid polymer in sulfonyl fluoride form with a compound selected from the group having the formula R-SO.sub.2 F, wherein R is a straight chain, branched or cyclic, highly fluorinated alkyl group having 1 to 30 carbon atoms. The impregnated film is irradiated with the radiation dose being in the range of 0.1 to 15 MRad. After irradiation, the film is hydrolyzed to form the membrane. The membranes have enhanced electrochemical properties when employed in electrochemical cells including improved performance under low humidity conditions.