Abstract: This invention provides a hot forming mold made of xonotlite group materials such as xonotlite, or wollastonite made therefrom, which are known as a heat-resisting materials. By hot pressing these material to high bulk density e.g., 0.6 to 2.20, a mold suitable for use in hot forming, having increased sending strength and hardness can be efficiently made.Such molds are made by filter pressing an aqueous slurry of xonotlite, then drying the pressed product to remove moisture at a temperature less than about 700.degree. C., and then cutting out the mold for use in molding plastic, glass and the like. By heat treating this mold product at a temperature of about 700.degree. to 1200.degree. C. the mold so produced can be subjected to machining and can be used as a mold for superplastic forming aluminum, titanium and the like.