A mixture of particulate silicone based material and small hollow elements, such as spheres and/or fibers, is provided. The particulate silicone based material is heated to a temperature between about 200.degree. F. and about 400.degree. F. The particulate silicone based material is cooled until a solid body is formed. The solid body is resistant to melting and thermal decomposition when heated to temperatures of at least 3000.degree. F. The solid body may contain cavities formed by the small hollow elements. The solid body may contain reinforcing fibers. The solid body may contain both small hollow elements and fibers.