The work presents an overview of the main properties of Hyflon (R) Ion perfluorosulfonic acid (PFSA) membranes for fuel cells in comparison with Nafion (R) PSFA membrane. The fuel cell performance of Hyflon (R) Ion-based membrane electrode assemblies (MEAs) is reported at medium (75 degrees C) and high (120 degrees C) temperature, demonstrating extremely good power output. Remarkable durability ( 5000 h) of the Hyflon (R) Ion product is also demonstrated in high power output conditions. The conductivity and the hydrogen permeability of Hyflon (R) Ion extruded membranes is reported in sub-freezing conditions (down to -40 degrees C). The degradation of the short-side-chain ionomer is investigated utilizing both ex-situ ( Fenton) tests and fuel cell open circuit voltage tests. In the latter, the influence of the operating temperature on Hyflon (R) Ion degradation is not detectable in the range analysed (70 degrees C-90 degrees C). A better resistance to degradation of chemically stable Hyflon (R) Ion membranes (" S"-grades) vs. standard membranes results from all tests.