TECHNOLOGY FOCUS - POLYMERS - Preferred Polymers: The structural film-forming or ionomeric polymer is in continuous phase. The polymer electrolyte membrane has coalesced morphology. The structural film-forming polymer is a fluorinated polymer such as terpolymer of tetrafluoroethylene, hexafluoroethylene and vinylidene fluoride, preferably copolymer of hexafluoropropylene and vinylidene fluoride having a film-forming temperature (Tff) of 180 degreesC or less and a melting point of 180 degreesC or less. The ionomeric polymer is a film-forming polymer such as fluoro polymer containing pendant sulfonic acid group. The Tff of the structural film-forming polymer is less than the Tff of ionomeric polymer by 15 degreesC or more.Preferred Method: The dispersion of ionomeric and structural film-forming polymer is cast and dried to form a cast mixture. The cast mixture is heated to the Tff of structural film-forming polymer or ionomeric film-forming polymer. The dispersion is partially dried to form a cast mixture and subsequently formed into a membrane. The structural film-forming polymer is cross linked subsequently. During coalescence of the structural film-forming polymer, the viscosity and volume fraction of the structural film-forming polymer (eta a,theta a), and the viscosity and volume fraction of the ionomeric polymer (eta b,theta b) in the cast mixture satisfy the relation theta a/theta b x eta a/eta b=1 within a variation of no more than 50%, or the relation theta a/theta b x eta a/eta b is less than 1. EXAMPLE - The dispersions of NafionSE10172 (Perfluorocarbon polymer, 11% solids 1100 equivalent weight) were mixed with THV 230R (RTM-terpolymer of 40% tetrafluoroethylene, 40% vinylidene fluoride and 20% hexafluoropropylene) and 35% solid dispersion of THV200. 5% of glycerol was added to the dispersion as a coalescing aid. A surfactant was added to stabilize the dispersion. The obtained dispersion was coated on a glass plate and dried at 80 degreesC and heated to 140 degreesC for 5-10 minutes to coalesce the film.    The cooled coated glass was submerged in water to release the film. The films had a thickness of 0.025 mm. The films were boiled in water, soaked in aqueous solution containing nitric acid and hydrogen peroxide at 60 degreesC and boiled in de-ionized water to stabilize the pH. The total membrane equivalent weight (EW) was calculated from the ratio of the constituents.    The ionic conductivity of the membrane composition comprising 100 weight % of Nafion (EW 1100) without adding THV was 150 mS/cm and the ionic conductivity of the membrane composition containing 50 weight % of Nafion (EW 1100) and 50% of THV was 40 mS/cm. The ionic conductivity was effectively reduced by the incorporation of THV. Equivalent weight of the total membrane was 2000 (50%THV) and moisture absorption was 10%. Addition of 30% or above THV gave the films sufficient stability and mechanical strength to withstand subsequent handling and testing.