TECHNOLOGY FOCUS - CERAMICS AND GLASS - Preferred Membrane: The coefficients of thermal expansion of the composite and metal film differ by less than 15%, preferably less than 10% and especially are about the same. The composite is 10-1000, preferably 20-200 micrometers thick and the metal coating is less than 5, preferably less than 2, especially less than 1 micrometer thick. The membrane is flexible and tolerates a flexure radius less than 100, preferably less than 10 mm. It is asymmetric, and its pores have an average diameter less than 500 nm, preferably up to 1 nm. The membrane may have a H2-permeable adhesion-promoting layer between the composite and the metal coating.Preferred Materials: The ceramic material is an oxide of titanium (Ti), zirconium (Zr), silicon (Si) and/or aluminum (Al); and the porous substrate comprises metal, glass or ceramic material, especially material with a mesh size of 5-500 micrometers and fiber or filament thickness of 20-70 micrometers.    TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: In stage (i), the composite is produced by the following stages:(a) hydrolyzing a hydrolyzable metal compound to a hydrolyzate;(b) dispersing the hydrolyzate by peptization with an acid;(c) mixing the dispersion with a nanocrystalline and/or crystalline metal oxide;(d) applying a thin layer of the mixture to a woven and/or nonwoven fabric;(e) consolidation to a composite at 100-680 degrees C; and(f) repeating (a) to (e) if necessary, using mixtures containing finer particles, to give a multi-layer composite, such that the metal oxide particles in the last layer applied have a radius not more than 1000 nm, preferably not more than 10 nm.An H2-permeable adhesion promoting layer may be applied before the metal coating. This layer or the thin layer of the mixture from stage (C), applied in stage (D), is applied by printing, pressing into or onto the substrate, rolling, spreading with a blade or brush, dipping, spraying or casting.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The hydrolyzable metal compound is a (oxy)nitrate, (oxy)chloride, carbonate, alcoholate, acetate or acetylacetonate of titanium (Ti), zirconium (Zr), silicon (Si) or aluminum (Al).    TECHNOLOGY FOCUS - METALLURGY - Preferred Materials: If the porous substrate comprises metal, this preferably is steel. The metal coating, which is permeable for H2, consists of palladium (Pd), silver (Ag), gold (Au), copper (Cu), cobalt (Co), nickel (Ni) ruthenium (Ru). rhodium (Rh), zinc (Zn), Al, Ti, Zr, indium (In), vanadium (V), tungsten (W), rhenium (Re), molybdenum (Mo) and/or rare earth metals, especially Pd or a Pd alloy, preferably with Ag or Cu, especially an alloy of 40-85 wt.% Pd and 15-60 wt.% Ag or Cu. EXAMPLE - Titanium isopropylate (40 g) was added to a mixture of (deionized) water (70 g) at 4 degrees C and ethanol (50 g) and the resultant precipitate was peptized with concentrated nitric acid (30 g). ca 3000 SG (RTM: alumina)(200 g) was dispersed in the resultant dispersion, giving dispersion (A). VP 25 (RTM: Zirconium oxide)(100 g) was dispersed in water (200 g), then 10 wt.% polyvinyl alcohol solution (molecular weight 72000 g/mole; 50 g), water (50 g) and zirconium nitrate sol (25 g) were added and dispersed, giving dispersion (B). A thin film of (A) was applied to a square mesh stainless steel fabric (180 mesh; 90 micrometers mesh size; 50 micrometers wire thickness) and hardened (2 minutes, 550 degrees C), giving a composite with average pore radius about 100 nm. A 50 micrometers thick layer of (B) was applied, dried and hardened (450 degrees C), giving a composite with pores of average radius 20-50 nm. Copper was applied to one side of this composite by sputtering to reduce the average pore radius to 5 nm. The composite was then electroplated with 500 nm palladium. At 200 degrees C, the hydrogen (H2) flow was over 1900 l/m2.hour and H2 permeated more than 30 times faster than nitrogen.