Film, fibre, foam and adhesive materials are produced from soluble S-sulfonated keratins. Once formed, the films, fibres, foams or adhesives are treated to modify the properties of the materials, in particular to improve the wet strength of the materials. Treatments used include removal of the S-sulfonate group by treatment with a reducing agent, treatment with an acid or treatment with a common protein crosslinking agent or treatment with a reduced form of keratin or keratin protein. The films are made by solvent casting a solution of S-sulfonated keratin proteins, the foam made by freeze-drying a solution of S-sulfonated keratin proteins and the fibres made by extruding a solution of a S-sulfonated keratin protein.