Abstract: A polyurethane pre-foam formulation having improved adhesion to polyester resins is disclosed. The polyurethane is of the type formed by the reaction of an isocyanate and a polyol together with a blowing agent. The improved formulation contains a polyester resin between about 1 and 10% by weight of the polyurethane together with a sufficient amount of a free radical catalyst to bring about a cure of the added polyester resin. Preferably, the improved polyurethane prefoam is foamed and cross-linked in contact with a partially uncured but gelled unsaturated polyester laminating resin which contains an unsaturated monomer such as styrene. When such a polyester and a polyurethane foam are cured together, a superior bond between them results when the polyurethane formulation is compounded in accordance with the teachings of the present invention.