NOVELTY - Proton-conducting, flexible electrolyte membrane for a fuel cell, which is impermeable for reaction components of a fuel cell reaction, has a flexible, perforated glass support, infiltrated with a proton-conducting gel suitable for selective conduction of protons through the membrane.    USE - The electrolyte membrane is used for producing a membrane electrode array or fuel cell (stack); and the membrane and array are used in fuel cells, especially direct methanol or reformate fuel cells (all claimed). Fuel cells with the membrane or array and mobile or stationary systems, especially a vehicle or domestic energy system, with the fuel cell (stack) are claimed per se.    ADVANTAGE - Existing membrane electrode arrays for fuel cells use organic polymers as proton-exchanging membrane but their conductivity depends on maintaining a suitable water content, which cannot be guaranteed at temperatures above 100degreesC and is generally impossible in reformate or direct methanol fuel cells. Existing inorganic proton conductors cannot be made into the thin membrane films with low surface resistance and high power density needed in lightweight cells. Electrolyte membranes of ceramic material on a metal support are unsuitable, as they tend to delaminate, whilst infiltration with sol usually leaves too much unfilled volume. The present membranes avoid these drawbacks. Their proton conductivity is higher than that of polymer membranes at low atmospheric humidity and of composites based on porous ceramics. The membrane electrode array has low total resistance and suitable mechanical properties, e.g. tensile strength and flexibility, for use under extreme conditions, e.g. in a vehicle, tolerates operating temperatures above 80 degrees C, avoids short-circuit and cross-over problems and can be produced easily.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) production of electrolyte membrane by infiltration of a flexible, perforated glass support with a mixture containing an immobilizable hydroxysilylalkyl-acid (I) of sulfur (S) or phosphorus (P) or its salt or a mixture containing a Bronsted acid and/or (I) or its salt and a sol precursor for aluminum (Al), silicon (Si), titanium (Ti), zirconium (Zr) and/or P oxide, followed by gelation;    (2) electrolyte membrane in this way;    (3) flexible membrane electrode array for a fuel cell, comprising the membrane and, on opposite sides, porous, electroconductive anode and cathode films comprising a catalyst for the anode and cathode reaction, a proton-conducting component and optionally a catalyst support;    (4) production of this array by coating each side of the electrolyte membrane, simultaneously or consecutively, with a mixture of a condensable precursor for the proton-conducting electrode layer, a catalyst (precursor) for the anode or cathode reaction and optionally a catalyst support and/or pore former and producing a firm bond between these layers;    (5) composition comprising a condensable component (II), which imparts proton conductivity after condensation of an anode or cathode layer of a membrane electrode array of a fuel cell, a catalyst (precursor) (III) for the fuel cell anode or cathode reaction, optionally a catalyst support, optionally a pore former and optionally an additive to improve foaming, viscosity and adhesion.    DESCRIPTION OF DRAWING(S) - The drawings are schematic sections of electrolyte membranes, comparing a commercial membrane with glass filaments surrounded by ceramic particles with a membrane in which ceramic particles are randomly distributed in an electrolyte gel.    Glass filaments (G)    Ceramic particles (K)    Electrolyte gel (E)