A seal material or buffer material including inorganic fiber paper includes first biosoluble inorganic fibers having an average fiber diameter of 3µm to 7 µm, second biosoluble inorganic fibers having an average fiber diameter of 2µm to 3 µm, and a binder, the average fiber diameter of the second biosoluble inorganic fibers being smaller than that of the first biosoluble inorganic fibers, wherein the chemical composition of the second biosoluble inorganic fibers is different from that of the first biosoluble inorganic fibers, and the first biosoluble inorganic fibers are SiO 2 /CaO fibers having an SiO 2 content of 50 mass% to 82 mass%, a CaO content of 5 mass% to 34 mass% and an MgO content of 1 mass% or less, or SiO 2 /MgO fibers having an SiO 2 content of 50 mass% to 82 mass%, an MgO content of 1 mass% to 20 mass%, and a CaO content of 1 mass% to 9 mass%.