The demand for a solid polymer electrolyte membrane for fuel-cell systems, capable of withstanding temperatures above 130 C, has prompted this study. A low-cost, highly conductive, nanoporous proton-conducting membrane, based on a polytetrafluoroethylene (PTFE) backbone has been developed. It comprises a nonconductive nano-size ceramic powder, PTFE matrix, and an aqueous acid. Impregnation of the ceramic powder into the PTFE matrix was carried out using sol-gel synthesis. The preparation procedures were studied and the membrane was characterized. This membrane demonstrated promising properties of high thermal stability (up to 300 degrees C), pressure-retention difference up to 2.2 bars, room-temperature conductivity up to 0.11 S cm(-1) (10-15% (w/w) SiO2, 3 M H2SO4), a hydrophilic/hydrophobic pore ratio of 1:1 and very high water flow at low pressure. A nonoptimized direct-methanol fuel cell with a 137 mu m thick membrane was assembled and tested. It produced 133 mW cm(-2) at 80 degrees C, 0.05 bars (g) dry air, 1.9 stoich (air), and 198 mW cm(-2) at 110 degrees C, 2.2 bars (g) dry air, 1.9 stoich (air). (c) 2007 The Electrochemical Society.