A composite high temperature insulator (A) includes a planar layer (10) having anisotropic thermal conductivity properties. A second planar layer (12) is formed from a rigid insulation material, such as a carbonized mixture of carbon fibers and a binder. The second layer is coextensive with the first layer and is preferably bonded thereto by a carbonaceous cement (44). When used to insulate a heat source, such as a furnace (50), convective heat is directed back to the source by the reflective surface (16) of the inner, anisotropic layer (10). Heat which enters the anisotropic layer is dissipated evenly through the plane of the layer along a plurality of heat paths defined by a plurality of layers (14) of flexible graphite. Accordingly, heat which reaches the outer, second layer (12) results in fewer hot spots than occur with a conventional rigid insulation material, thereby reducing the total amount of insulation material required to achieve a desired level of thermal insulation.