The present invention relates to a method of fabricating an insulating resin material (4) from a core/shell particle (3) having a core particle (2) containing a macromolecular compound and a shell layer (1) coating the core particle (2) and containing an inorganic compound. The method of fabrication includes mixing the core/shell particles (3) with a good solvent (10) for the macromolecular compound, infiltrating the good solvent (10) through the shell layer (1), impregnating the good solvent (10) into the macromolecular compound, molding a compact from the impregnated core/shell particles (3), and removing the good solvent from the compact by heating the molded compact.