We report thermal and transport properties of commercial membranes Nafion 117 (Dupont) and PBI (Celanese) and 2,5-benzi-imidazole (ABPBI), a modified PBI polymer prepared by polymerization of 3,4-diaminobenzoic acid with polyphosphoric acid. The PBI membranes were prepared by casting of a solution of the polymer powder dissolved in dimethylacetamide, while the ABPBI membranes were casted from its solution in methanesulphonic acid. The imidazole-based membranes were protonated by immersion in concentrated solutions of H3PO4. The low temperature thermal behavior of Nafion, PBI and ABPBI membranes with different water contents and equilibrated with water-methanol mixtures of different concentrations were studied by differential scanning calorimetry (DSC). For Nafion, the DSC curves revealed a weak transition at temperatures below –100 oC, related to the true glass transition temperature of the polymer. The freezing of water in Nafion containing water-methanol takes place at temperatures in the range of –10 to –20 oC, being relevant to the operation of direct methanol PEM fuel cells in low temperature environments. The amount of freezable water, that could be a criteria for choosing membranes for DMFC beyond the methanol permeation characteristics, was determined from the area of the ice fusion peak and it increased from 1 to 23 % as the relative humidity increases from 84 to 100%. The presence of methanol in the membrane increased the amount of freezable water up to 65%. The methanol permeation and the electrical conductivity of Nafion, PBI and ABPBI membranes were determined as a function of temperature up to 90 oC in order to compare their performance in conditions close to those corresponding to PEM and direct methanol PEM fuel cells. The methanol permeation, measured with a two-chamber cell, in ABPBI membranes is much lower than in Nafion and slightly higher than in PBI. The electrical conductivity of the membranes was measured using a DC four electrodes method. The conductivity of PBI and ABPBI membranes, which is a function of the degree of H3PO4 doping, reaches values as high as in Nafion under similar conditions of temperature and water content.