TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: The method may include treating the substrate with hydrophobic polymer and sintering the treated substrate prior to application of first loading composition; compacting and drying the substrate and first loading composition, or drying and compacting the substrate and first loading composition prior to application of second loading composition; and compacting the substrate and second loading composition after second application step. At least 50% (preferably 75%) of the total loading material is applied in the first application step, and 25-50% of the total loading material is applied in the second application step. The substrate and loading material are compacted at 50-200 psi. At least one of the application steps includes applying the loading material to a release material, and contacting the substrate and release material so that the loading material is disposed between the substrate and release material. In alternative embodiments, the fluid-diffusion layer is manufactured by applying a loading composition to the substrate, partially drying the substrate and loading composition, compacting the substrate and loading composition, and further drying the substrate and loading material; or applying a loading composition to the substrate and/or release material so that a coated surface is formed, contacting the substrate and release material so that the coated surface is disposed between them, compacting and drying the substrate, release material and loading composition, and removing the release material from the substrate and loading material. The loading material is adhered to the substrate at at most3 (preferably at most2.3) mg/cm3. An electrocatalyst may be deposited to the fluid-diffusion layer to form an electrode.Preferred Properties: The fluid-diffusion layer has an average surface roughness of less than 13 (preferably less than 10) mum as determined by a Wyko NT2000 3-D optical profiler. Prior to application of loading composition, the substrate has an average surface roughness of at least16 mum, an average pore size of at least30 mum, and an initial porosity of at least80%.Preferred Components: The first and second loading compositions are identical. Each loading composition has a solids content of less than 20%. The substrate is carbon-fiber non-woven substrate or carbon paper substrate.