Abstract: A process for utilizing compact or porous plastics is described that comprise in part or totally polyurethane plastics, wherein the process is characterized by the fact that the plastics are prepared into a reaction mixture with a low hydroxyl number, which can be further processed in the conventional manner into new final products by swelling the plastics eithera) in suitable swelling agents and reducing in size into a free flowing gel; orb) dissolving and/or decomposing in suitable hydroxy polyols; andc) adjusting the hydroxyl number to the desired size;d) optionally transforming the reaction mixture comprising a), b) and c) into a polyurethane prepolymer,e) further processing the individual reaction mixtures a) to c) into a polyurethane product or into a plastic with the aid of other suitable hardener systems.