The present invention relates to a process for improving the waterproofing of hides, skins, leathers, and furs, as well as other fibrous materials, by treatment with special surfactants in the beamhouse and/or in the treatment of the wet blues, prior to waterproofing. Particularly suitable as surfactants are anionic surfactants based on salts of N-acyl-amino acids and nonionic surfactants, such as alkyl polyglycosides or polyethyleneglycol carboxyalkyl ethers. The surfactants are used in amounts of 0.5 to 5% wt., relative to the pelt or shaved weight.