NOVELTY - The method comprises coating a porous conductive substrate with a hydrophobic fluorocarbon polymer, contacting the fluorocarbon coated substrate with a silicone composition, and applying a microporous layer to a side of the substrate. The porous conductive substrate is coated by contacting the substrate with a coating composition comprising a solvent and particles of a hydrophobic fluorocarbon polymer, removing the solvent, sintering the particles, and loading the substrate with 3-10 wt.% of the fluorocarbon particles based on the total weight of the coated substrate.    USE - The method is useful for making a diffusion medium for a proton exchange membrane fuel cell, which is useful as a power source for electric vehicles and other applications.    ADVANTAGE - The method is capable of efficiently and reliably making the diffusion medium with high performance and enhanced hydrophobic properties thus producing fuel cell with high reactant and product permeability, humidity performance and current stability, good electronic conductivity and heat conductivity and improved mechanical strength.    DETAILED DESCRIPTION - The method comprises coating a porous conductive substrate with a hydrophobic fluorocarbon polymer, contacting the fluorocarbon coated substrate with a silicone composition, and applying a microporous layer to a side of the substrate. The porous conductive substrate is coated by contacting the substrate with a coating composition comprising a solvent and particles of a hydrophobic fluorocarbon polymer, removing the solvent, sintering the particles and loading the substrate with 3-10 wt.% of the fluorocarbon particles based on the total weight of the coated substrate. The fluorocarbon coated substrate is contacted by spraying the silicone composition onto the substrate. The microporous layer comprises fluorocarbon polymer and conductive particles. An INDEPENDENT CLAIM is included for a method for improving the high humidity performance of a proton exchange membrane fuel cell stack.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a fuel cell stack.    Bipolar fuel cell stack (2)    Pair of membrane electrode assemblies (4, 6)    Bipolar plate (8)    End contact elements (14, 16)    Storage tank. (46, 48)