TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Distributor: The contact layer is 5-100 microns thick and the carbon (C)carrier 100-400 microns thick.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: Both hydrophobic layers contain polyethylene (PE), polypropylene (PP) and/or polytetrafluoroethylene (PTFE) and either (a, b) contain 10-45 weight % of (a) C fibers or finely-divided C particles and are 5-40 microns thick; or (c) penetrate the C carrier to a depth of 5-40 microns and preferably fill 40-60 % of the pore volume in this region. The contact layer contains an intimate mixture of 40-90 weight % finely-divided C particles and PE, PP and/or PTFE as hydrophobic polymer(s). Production: (all claimed) The hydrophobic layers are produced by: (a) coating both sides of the carbon (C) carrier in turn with a paste of hydrophobic polymer powder, C fibers and a liquid phase and drying, then calcining the 3-layer structure to sinter the polymer; (b) coating both sides of the C carrier in turn with a paste of hydrophobic polymer powder, finely-divided C power and a liquid phase and drying, then calcining the 3-layer structure to sinter the polymer; (c1) coating both sides of the C carrier in turn with a paste of hydrophobic polymer powder and a liquid phase and drying, then calcining the 3-layer structure to sinter the polymer; (c2) placing a thin film of hydrophobic polymer on both sides of the C carrier and bonding by applying pressure and heat; (c3) impregnating the C carrier on both sides with a dispersion containing hydrophobic polymer and drying in air, then calcining to sinter the polymer. In all methods, one side is then provided with a contact layer, by applying an ink containing a hydrophobic polymer and fine C particles, drying and calcining again. EXAMPLE - To produce a substrate (A1) for anode gas distributors, carbon (C) fiber paper (TGP-H-060 RTM; porosity 74.1%; thickness 200 microns) was coated on one side with a paste of 5 g Hostaflon TF1740 (RTM; polytetrafluoroethylene (PTFE) powder; average particle size 25 microns) and 1 g Shellsol D70 (RTM) and dried in air at 100 degrees C. The back was then coated in the same way, then the PTFE was sintered for 15 minutes at 340-350 degrees C, giving 21.15 g PTFE/m2. A substrate (A2) for cathode gas distributors was produced in the same way, except that the paste contained 2 g Shellsol D70 (RTM) and the PTFE loading was 10.63 g/m2. For controls, the C fiber paper was immersed for 10 minutes in aqueous PTFE dispersion (Hostaflon TF 5032 RTM), drained, dried in air for 10-15 minutes and sintered for 10-15 seconds on a hot plate at 350 - 410 degrees C to give an anode substrate (B1) with 9.3 weight % PTFE and cathode substrate (B2) with 4.5 weight % PTFE. Inks for the contact layer of the (a) anode and (b) cathode structure contained (a) 12.88, (b) 12.65 g Russ XC72 (RTM; C black), (a) 52.52, (b) 50.28 g dipropylene glycol, (a) 25.16, (b) 24.37 g 16.7% solution of Mowital B20H (RTM) in dipropylene glycol n-butyl ether, (a) 0, (b) 2.95 g polyethylene oxide (molecular weight 300000), (a) 9.08, (b) 9.22 g Hostaflon TF 5032 (RTM; aqueous PTFE dispersion) and (a) 0.36, (b) 0.32 g deionized water. The inks had a viscosity of (a) 1.1, (b) 10.5 Pa s at 100/second and dry residue of (a) 22.5, (b) 25.2 weight %. They were screen printed on the treated carriers and dried at 100 degrees C. The structures were then heated in a muffle furnace at 390 degrees C for 1 hour, when the weight of the contact layer decreased by (a) 18.5, (b) 28.5%, giving 2.5 mg/cm2 calcined contact layer with a thickness 15-20 microns. Both sides of the structures had a coarsely porous hydrophobic layer, mainly of PTFE, with a thickness of (a) 12-15, (b) 5-10 microns, corresponding to 54-58 wt.% PTFE on the C fiber substrate. The fibrous nature of the paper ensured conductivity and the porosity was high enough for gas transport. The residual porosity of the hydrophobic layers was about 53% of the original pore volume. Fuel cells with an active cell area of 50 cm2 were made using anode and cathode structures based on (A) (A1) and (A2) or (B) (B1) and (B2). In operation in reformate/air at 600 mA/cm2, the cell potential was (A) 629, (B) 560 V. Hence (A) gave much more power than (B).