To obtain an excellent heat insulation performance with further reduced thermal conductivity without using fluorocarbon by using calcium silicate molding containing a specific ratio of inorganic fiber as a heat insulation core material.

A calcium silicate molding containing 5 to 40wt.% of inorganic fiber is used as a heat insulation core material. A diameter of the fiber is normally 1 to 20μm and a length is normally 1 to 20mm. The fiber includes, for example, alumina fiber, ceramic fiber, carbon fiber, glass fiber, and rock wool, and the glass fiber is preferable. Siliceous raw material is amorphous or crystalline, and includes, for example, natural material such as diatomaceous earth, silica or quartz or industrial by-product such as silicon dust, or silica. The core material preferably contains a radiation heat absorbing material. Since the core material is a molding, in the case of discarding it, no environmental problem due to dust generation occurs.