TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred materials: The functional film contains at least one component from: (a) a zeolite and/or zeolite analogue (A); (b) inorganic oxide fine particles; (c) a silicone rubber, resin or oil; (d) an organic polymer compound; and (e) carbon (esp. (A) having the top surface coated with a silicone compound). (A) is a 96 % silica and/or pure silica zeolite. The porous support comprises mainly ceramic and has less than 0.5 mum average pore diameter. The zeolite film is MFI type which satisfies a/b = 0.3-1.5 and b/c is greater than 4.4 (a, b, c = highest peak intensities at 2 approximately q = 7.3-8.2 degrees, 8.5-9.1 degrees and 13.0-14.2 degrees, respectively, in the X-ray diffraction pattern measured with a parallel optical system using 1.54 Angstrom CuK alpha X-rays, 3 degrees incident angle and 2 approximately q 4 degrees/min scan rate) (esp. at most 3 mum thick).Preferred film: After baking, the room-temperature hydrogen permeation rate difference before and after contacting with ethylene glycol saturated vapor at 85 degreesC for 24 h is at most 2 x 10-7 mol/m2.s.Pa.Preferred method: The filmy material is prepared by contacting a porous support with a zeolite or zeolite analogue seed crystal, and then coating a silica solution, slurry or colloid. The steam treatment is at 80-200 degreesC. EXAMPLE - 0.28 g NaOH was added to 20 g of a 20-25 wt.% aq. solution of tetrapropylammonium hydroxide (TPAOH), stirred, 5 g fumed silica added, heated at 80 degreesC to give a transparent solution, then at 125 degreesC for 8 h, to give fine particles of silica light (80 nm average particle diameter), and water added to give an 8 wt.% silica light colloid. 0.1 g this was coated onto an alpha-alumina porous support (3 mm thick; 1.4 cm square; 0.1 mum average pore diameter; surface treated with alumina powder), dried, and baked at 550 degreesC for 3 h, to give a coating of seed crystals. This was immersed in a gel (fumed silica:TPAOH:H2O = 40:12:16800) and heated at 130 degreesC for 24 h, to form a 2 mum thick film of silica light on the support, then baked at 550 degreesC for 2 h (0.6 degreesC/min ramp up; 1.2 degreesC/min ramp down). The film was placed between 2 glass tubes (inner diameter = 10 mm) and sealed with epoxy resin adhesive, to give a permeation test cell (0.785 cm2 surface area). The cell gave 1.9 CB/AD value (A, B = hydrogen and water in the supplied gas, and C, D = hydrogen and water in the permeated gas, respectively) and 2.0 x 10-7 mol/s.m2.Pa hydrogen permeation rate in the presence of water vapor at room temperature, constant for at least 4 h.