A prepolymer system has a monomeric isocyanate content of no greater than about 10% by weight based on 100 parts by weight of the prepolymer system. The prepolymer system comprises a diluent component and a prepolymer component different than and separate from the diluent component. The diluent component has an excess of isocyanate (NCO) functional groups, and comprises the reaction product of a monohydric isocyanate-reactive component and an excess of a first isocyanate component. The first isocyanate component comprises monomeric isocyanates reactive with the monohydric isocyanate-reactive component. The prepolymer component also has an excess of NCO functional groups, and comprises the reaction product of a polyol component and an excess of a second isocyanate component. The prepolymer system can be used to prepare foams via reaction with water. The foams have low density and have excellent adhesion and sound dampening properties for use in cavities of automobile bodies.