NOVELTY - Electrolyte membranes of high proton conductivity with a ceramic composite, good tensile strength and flexibility under extreme conditions, e.g. in automobiles, toleration of a high operating temperature, and no cross-over or short-circuit problems can be obtained if, in place of the conventional MF-membranes, a glass fabric or nonwoven is used as carrier, based on a polymer fiber substrate infiltrated with electrolyte.    USE - The EM are useful for fuel cells (claimed), i.e. direct methanol fuel cells or reformate fuel cells (claimed), or for the preparation of membrane electrode units of a fuel cell or fuel cell stack (claimed), and for microfiltration.    ADVANTAGE - The EM have high proton conductivity with a ceramic composite, good tensile strength and flexibility under extreme conditions, e.g. in automobiles, toleration of a high operating temperature, no cross-over or short-circuit problems, and avoid a drawback of previous EM, i.e. lack of long term stability and high cost of membranes based on glass fabric.    DETAILED DESCRIPTION - A non-permeable, proton conductive, flexible electrolyte membrane (EM) for a fuel cell including a flexible, material permeable composite material as carrier, with a flat flexible substrate with a number of holes and with a coating applied on and in it, where the substrate material is selected from woven or unwoven polymer fibers and the coating is a porous ceramic, while the carrier is infiltrated with a proton conductive material suitable for selective conduction of protons through the membrane.    INDEPENDENT CLAIMS are included for:    (1) a process for preparation of the EM by:    (a) infiltration of a carrier based on a material permeable composite, with a number of holes etc, as above, where the ceramic is coated with a mixture (a1) containing an immobilizable hydroxysilylalkyl acid of sulfur or phosphorus or a salt of the acid, or (a2) a mixture containing a Bronsted acid and/or an immobilizable hydroxysilyalkyl acid of sulphur or phosphorus or a salt of the acid, and a sol which includes a pre-stage for aluminum, silicon, titanium, zirconium, and/or phosphorus oxides, or (a3) a mixture containing zirconium and/or titanium phosphate, phosphonate and/or sulfonate, and optionally a sol, which is a pre-stage for aluminum, silicon, titanium, zirconium, and/or phosphorus oxides as a network builder, and    (b) stabilization of the mixture infiltrating into the carrier, to provide an infiltrating proton conductive material for the carrier suitable for selective conduction of protons through the membrane;    (2) a flexible membrane electrode unit for a fuel cell, with an electrically conductive anode and a cathode, with impermeable flexible EM for the fuel cell on opposite sides for the reaction components, where the EM has a flexible material permeable composite as carrier as described above, a flexible substrate coated as above, the anode and cathode layers are porous, and a catalyst for the anode and cathode reactions, a proton conductive component, and a catalyst support;    (3) a process for preparation of the membrane electrode unit by (A) preparation of an impermeable proton conductive, flexible membrane for the fuel cell, with a carrier, substrate, with a porous ceramic coating as described above, (B) preparation of an agent for preparation of the anode and cathode layers including (B1) a condensable component which after condensation removes the proton conductivity of the electrode layers, (B2) a catalyst which catalyzes the anode or cathode reactions or a pre-stage compound of the catalyst, (B3) optionally a catalyst support, (B4) optionally a pore former, (C) application of the agent of stage (B) to one side of the EM as stage A of coating formation, (D) creation of a solid composite between the coatings and the EM, with formation of a porous proton conductive anode or cathode layer, where the anode and cathode layers can be formed simultaneously or in succession; and    (4) a fuel cell with an EM, a stationary or mobile system with an EM unit, a fuel cell, and a fuel cell stack containing an EM.