To provide a light heat insulating material, which enhances heat insulating property by greatly suppressing heat transfer of a bone structure and heat-transfer caused by a convection current in a foamed body, and also to provide a preparation process of the same.

The foamed body is prepared by mixing 100 pts.mass of polyol and 5-50 pts.mass of water as a foaming agent and setting an isocyanate index in the range of 30-80. The above foam is compressed so that the density is to be 10-50 kg/m3 and the cell diameter toward the direction of compression to be under 1,000 μm.