A polyurethane foam which is obtained from an inert gas and a polyurethane reaction composition containing a polyol component, a foam stabilizer, a catalyst and an isocyanate component, by a mechanical froth method, wherein: the polyol component contains a polymer polyol having a solid content of from 20% by weight to 43% by weight; and the polyurethane reaction composition contains an acid-modified polyolefin powder.

A polyurethane prepolymer composition may include: (a) a polyurethane prepolymer comprising, as a reaction product, (a1) an excess of diisocyanate and (a2) a polyol; and (b) free diisocyanate monomer in a range of from more than 0 to less than 1.0 wt. %, based on total polyurethane prepolymer weight. The NCO content of the polyurethane prepolymer may be in a range of from 0.2 to 15 wt. %. The polyurethane prepolymer may include less than 75 wt. % of a 2:1 stoichiometric adduct of the diisocyanate and the polyol, based on the total polyurethane prepolymer weight. The polyol (a2) may include two polypropylene glycols with different molecular weights.

In the present invention, there is provided an urethane resin composition containing an urethane resin (A), water (B), and a surfactant (C) having no aromatic ring, and having a hydrophobic portion having 10 or more carbon atoms, wherein the urethane resin composition has a carbonate structure (X) and an oxyalkylene structure (Y) derived from the urethane resin (A). Further, the present invention provides a foamed urethane sheet which is formed from the urethane resin composition, wherein the foamed urethane sheet has a density of 200 to 1,000 kg/m.sup.3. The urethane resin composition according to claim 1, wherein the mass ratio of the carbonate structure (X) to the oxyalkylene structure (Y) [X/Y] is in the range of from 10/90 to 90/10.