Hard polyurethane foam, preparation method and application thereof

The invention provides hard polyurethane foam, the preparation method and the application thereof. The hard polyurethane foam of the invention contains expandable graphite of 20 to 325 meshes accounting for 1 percent to 30 percent by weight. The hard polyurethane foam also has low coefficient of heat conductivity and high porosity by closed pore besides desirable flame retardant property. The smoke density of the hard polyurethane foam is 10 percent to 40 percent (SDR); the horizontal firing speed is 0.10m/s to 0.35m/s; the coefficient of heat conductivity ranges from 0.0180w/m*k (at 25 DEG C), and the porosity by closed pore is more than 85 percent.