Mica based high insulating coat and silica based normal insulating coat were prepared as a test coat. Plate aluminum alloy AC2A was cast using a cast iron mold coated with the test coat. The thermal conductivity of the coat was estimated from the relationship between the solidification time of the casting and the coat thickness. It was found that the thermal conductivity of the high insulating coat was about 30 percent of that of the normal insulating coat. The aluminum alloy plate was cast by the evaporative pattern casting process using the expanded polystyrene pattern coated with the test coat. When the silica sand was packed and the high insulating coat was coated with a pattern 1 mm thick, the experimental value of the solidification time increased by about 20 percent, and the calculated value of the heat absorption by the mold reduced by about 20 percent, respectively, compared with when the normal insulating coat was coated. The effects of the high insulating coat on the solidification time and heat absorption by the mold increased with increasing coat thickness. When the steel shot was packed, these effects were more marked than when the silica sand was packed. With a practical coat thickness, the effects of the high insulating coat on the solidification time and heat absorption by the mold were smaller than the difference between the thermal conductivity of the high insulating coat and that of the normal insulating coat
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