A moldable heat insulating composition, a shaped heat insulator using the composition, and a method for manufacturing the heat insulator are disclosed. The composition can provide a heat insulator with heat resistance and heat insulating ability against a thermal equipment elevating to high temperatures thanks to high heat insulating ability of silica aerogel, and attachable to complicated shaped equipments. The composition comprises (A) silica aerogel having a porosity of 60% or more, (B) starting material liquid for forming a ceramic crystal via hydrothermal reaction (starting material liquid for hydrothermal synthesis), (C) surfactant, and (D) reinforcing fiber.