Abstract: A heat-resistant, highly expansible sheet material for supporting a catalyst carrier containing unexpanded vermiculite, in which the cations contained between the layers of the vermiculite are at least partly exchanged by ammonium cations, is provided. A process for the preparation of the sheet material, which involves blending an unexpanded vermiculite which has been preliminarily immersed in an aqueous solution containing alkali metal ions, inorganic fiber, an organic binder, and an inorganic binder, whereto a slurry solution of beaten natural organic fiber is added, and forming a sheet material from the mixture, is described.