TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Layers: The heat generation material layer consists of a raw material, which generates heat by irradiation of microwave, and a water absorptive pigment having water absorptivity of 1-60%, in 50% relative humidity. The thermal storage material layer consists of a microcapsule solid substance having a thermal storage material.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Layers: The heat generation material layer consists of a raw material, which generates heat by irradiation of microwave, and a water absorptive pigment having water absorptivity of 1-60%, in 50% relative humidity. The thermal storage material layer consists of a microcapsule solid substance having a thermal storage material.    TECHNOLOGY FOCUS - POLYMERS - Preferred Layer: The heat insulation layer contains polyolefin-type material. EXAMPLE - 5% sodium salt aqueous solution (5 g) of styrene-maleic acid anhydride copolymer was stirred with paraffin wax (80 g) of melting point 50degreesC, and emulsified. Melamine (5 parts), 37% formaldehyde aqueous solution (7.5) and water (15) were mixed, and melamine-formalin initial stage condensate aqueous solution was prepared. The obtained aqueous solution was added to the emulsified liquid, and heat-stirred at 70degreesC for 2 hours. Capsulation reaction was performed, and microcapsule of volume average particle diameter 5.2 microns was obtained. Powder processing of the microcapsule dispersion liquid was carried out, and polyvinyl alcohol aqueous solution (20 parts) was added, extruded and dried. A thermal storage material granulated substance was obtained. A package made from cotton was packed with the granulated substance (500 g), and a thermal storage material layer was obtained. A package made from cotton was packed with silica gel particle (500 g) of diameter 2 mm and moisture content 12%, and a heat generation material layer was obtained. A heat insulating material layer was formed using a foam polyethylene resin of thickness 8 mm. The heat insulating material layer, the heat generation material layer and the thermal storage material layer were laminated sequentially, and covered by the package made from cotton. A heat insulating material was obtained. The heat insulating material had improved heat-retaining property for long period of time.