A resin composition for use in a froth spraying system for forming polyurethane foam is disclosed. The resin composition comprises a Mannich polyol, at least one additional polyol other than a Mannich polyol, and a physical blowing agent. The Mannich polyol has a viscosity of at least 4,000 centipoise at 25° C. The physical blowing agent is selected from the group of volatile non-halogenated C2 to C7 hydrocarbons, hydrofluorocarbons, hydrochlorocarbons, and mixtures thereof. The physical blowing agent is present in an amount of greater than 10 parts by weight based on 100 parts by weight of the resin composition. A method of forming the polyurethane foam is also provided comprising the steps of providing the resin composition and a polyisocyanate, mixing the resin composition with the polyisocyanate in a mixing chamber to form a mixture, and discharging the mixture from a dispensing gun as the resin composition reacts with the polyisocyanate to form the polyurethane foam.