PURPOSE: A fireproofing polyisocyanurate foam that is prepared by combining an inorganic fibrous material, inorganic porous particles and a specific foaming inorganic material, etc.

CONSTITUTION: (A) a foaming material consisting of polyol, organic polyisocyanate, polymerization catalyst, foaming agent, etc., (B) an inorganic fibrous material, as glass fiber or rock wool, (C) inorganic porous particles as pearlite or sirasu baloon, (D) a foaming inorganic material forming an inorganic foaming layer by melting at high temperature to gasify the crystal water and gradually foaming to swell, and (E) an inorganic material which is obtained by reducing the crystal water content in the above inorganic material (D) to 1/2 are mixed, charged in a mold and foamed by heating.