Abstract: A first object of the present invention is constituted by regenerated cellulose based materials, in particular those selected from cellular cellulose materials, fibers, filaments, sheets, textiles and non-woven materials. They contain an effective quantity of at least one chemical agent which improves the resistance of the material to bleach; the chemical agent containing in its structure at least one nitrogen atom .alpha. to a carbon atom and being fixed by at least one covalent bond to the cellulose lattice and/or being trapped in said lattice. Further objects are constituted by the use of chemical agents to improve the resistance to bleach of regenerated cellulose based materials, in particular sponges, and a process for the preparation of these materials.