Non-fluorinated blocked polyurethanes are described as extenders and, particularly as textile auxiliaries, for use with fluorochemical polymers in treating substrates, for example fibrous substrates, such as textile fabrics or yarns. The polyurethane is prepared by reacting a polyisocyanate, a blocking agent, and a non-fluorinated isocyanate reactive compound having an average alkyl chain length of 24 to 50 carbon atoms.