TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: Forming the sheet includes disposing the stretched carbonaceous filaments on a surface of a substrate. The substrate is at least partially wound around a collector when the stretched filaments are disposed on the substrate. The method is a reel-to-reel type method. The method comprises heating the carbonaceous material to 250-400degreesC, before extruding the carbonaceous material.Preferred Dimension: The substrate is 0.02-0.25 mm thick. The gas diffusion layer is 0.05-0.65 mm thick. The stretched carbonaceous filaments have an average diameter of 0.5-15 microns, an average length of greater than or equal to1, preferably greater than or equal to50 mm. The sheet is 0.02-0.5 mm thick.Preferred Property: The fuel gas diffusion layer has a flexural strength of greater than or equal to300 pounds/square inch, a strength of greater than or equal to4 pounds/inch, in-plane resistivity of less than or equal to50 mOmega-cm, a through-plane resistivity of less than or equal to200 mOmega-cm, and a porosity of greater than or equal to30%. The sheet has a basis weight of 10-200 g/m2.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: Forming the sheet includes disposing the stretched carbonaceous filaments on a surface of a substrate. The substrate is at least partially wound around a collector when the stretched filaments are disposed on the substrate. The method is a reel-to-reel type method. The method comprises heating the carbonaceous material to 250-400degreesC, before extruding the carbonaceous material.Preferred Dimension: The substrate is 0.02-0.25 mm thick. The gas diffusion layer is 0.05-0.65 mm thick. The stretched carbonaceous filaments have an average diameter of 0.5-15 microns, an average length of greater than or equal to1, preferably greater than or equal to50 mm. The sheet is 0.02-0.5 mm thick.Preferred Property: The fuel gas diffusion layer has a flexural strength of greater than or equal to300 pounds/square inch, a strength of greater than or equal to4 pounds/inch, in-plane resistivity of less than or equal to50 mOmega-cm, a through-plane resistivity of less than or equal to200 mOmega-cm, and a porosity of greater than or equal to30%. The sheet has a basis weight of 10-200 g/m2.