Favorable performance of diffusion media in fuel cells has found to be correlated to a parameter (the C/F ratio) that relates to a spatial and thickness distribution of the hydrophobic fluoropolymer on the carbon fiber substrate structure of the medium. Suitable diffusion media may be chosen from among commercially coated diffusion media by measuring the C/F ratio by means of energy dispersive spectroscopy, and choosing the diffusion media if the value of the C/F ratio is within the preferred range. Alternatively, the diffusion media may be manufactured with an improved process that consistently yields values of C/F ratio in the desired range.