an assembly consisting of at least one seal layer and a solid polymer ion exchange layer wherein the seal layer covers essentially only the region of the ion exchange layer which is to be sealed . the seal layer is made of porous polytetrafluoroethylene film having one surface coated and partially impregnated with a solid polymer ion exchange material . the seal layer provides support and masking functions for the solid polymer ion exchange layer during intermediate manufacturing steps , and reinforcement and effective sealing when assembled in an electrochemical apparatus .