Polyurethane foam is a polymer made of isocyanate and polyether as the main raw materials, under the action of foaming agents, catalysts, flame retardants and other additives, mixed by special equipment, and foamed on site by high-pressure spraying. Polyurethane foam includs flexible foam, rigid foam and semi-rigid foam. Semi-rigid foam and flexible foam are open-cell structures mostly, and rigid foam is closed-cell structures mostly.