Abstract: Fuel cell having: (a) an anode; (b) a cathode; (c) a polymer electrolyte membrane placed between the anode and the cathode which has at least one polyolefin grafted with a side chain containing proton conductive functional groups; wherein said fuel cell has a value of cell resistance at 90° C. not higher than 0.30 ?cm2, preferably having between 0.2 ?cm2 and 0.25 ?cm2, more preferably between 0.05 ?cm2 and 0.20 ?cm2; a value of cell resistance at 20° C. differing from the value of cell resistance at 90° C. of an amount not higher than 90%, preferably not higher than 70%, more preferably not higher than 50%, with respect to the value of cell resistance at 90° C. Preferably, said fuel cell is a direct methanol fuel cell (DMFC).