Process for preparing a polyurethane backed substrate whereby a polyurethane forming mixture comprising at least one polyahl, at least one polyisocyanate and at least one catalyst for the urethane forming reaction is applied to a substrate and subsequently curing thereon to form an attached polyurethane backing. The process is characterized by employing as the catalyst an organoiron or organobismuth catalyst. The organoiron or organobismuth catalyst is advantageously employed in an amount such that the polymer-forming mixture exhibits the viscosity of not greater than 20,000 cps (20 Pa.s) 2 minutes after the polyahl and the polyisocyanate are contacted in the presence of said organoiron or organobismuth catalyst at a temperature between 20 and 50 C and the polyurethane forming mixture cures at a temperature between 100 and 150 C to a tack free state in less than 8 minutes after the polyahl and the polyisocyanate are contacted in the presence of said organoiron or organobismuth catalyst.