PURPOSE: To improve heat insulating and retaining performance at a casting temp. by using ceramic fibers and substituting part of a top part heat retaining material having a specific compsn. with said fibers.

CONSTITUTION: The compsn. of the top part heat retaining material contains 10W50wt% M.Al, 15W50wt% Al2O3, 5W30wt% SiO2, ≤20wt% FeO+Fe2O3, 5W13wt% T.C and assistants such as binder and ignition additive. The ceramic fibers are used and part of the above-mentioned Al2O3 and/or SiO2 is substd. with said fibers. The increase rate of the heat conductivity at the casting temp. is thereby decreased and the heat insulating and retaining performance is improved, by which the generation of cold shot segregation is prevented.