To quickly, easily, and safely install a heat insulating body by integrally molding the heat insulating body for an elbow while providing a hollow elbow hole in its substantial center and arranging a slit reaching the hollow elbow hole along the longitudinal direction of the molding body.

In an integrated heat insulating body 1 for an elbow is integrally molded of inorganic fiber so that a hollow elbow hole 2 is arranged in its substantial center, and a slit 4 reaching the hollow elbow hole 2 is arranged along the longitudinal direction of the molding body 3. In this way, an elbow part in a pipe can be easily housed in the hollow elbow hole 2 via the slit 4, so that heat insulation work can be facilitated. In manufacture of this kind of heat insulating body 1 for an elbow, a curved pipe type mandrel, for example, surrounded by inorganic fiber with a predetermined thickness is clamped by a pair of split dies having outer circumference parts formed symmetrically, and under this condition, a binder stuck to the inorganic fiber is hardened by heating for turning the inorganic fiber into the molding body 3, and then, the mandrel is removed.