A novel flexible non-woven carbon fibre gas diffusion substrate comprising a plurality of first carbon fibres orientated in the x-, y- and optionally z-directions, said first fibres being bonded with a thermoplastic polymeric substance, and a carbon based filler material, characterised, in that the flexible non-woven carbon fibre gas diffusion substrate has a total density of greater than 0.35 g/cm³, and a gas diffusion electrode obtained therefrom is disclosed. Also disclosed is a process for the manufacture of the substrate and electrode.