PURPOSE: To prevent the generation of a shrinkage in a thick part in the production of the casting having a variable-thickness part by mixing a hollow refractory grain with the apparent density and diameter specified and a solid refractory aggregate having a specified grain diameter to form the heat insulating pad.

CONSTITUTION: Thirty to 95 pts.wt. of the hollow refractory grain having ≤0.8g/cm3 apparent density and 0.07-0.8mm average diameter and 5-70 pts.wt. of the solid refractory aggregate grain having 0.01-0.2mm average diameter are mixed to prepare the material for producing a heat insulating pad for casting. The heat insulating pad is obtained by adding 2-10 pts.wt. of a curable binder to 100 pts.wt. of the material and forming the mixture into a desired shape. The gap between the hollow refractory grains is filled with the solid refractory aggregate grain to improve the strength of the formed body. Since the pad is generally resistant to fire, the casting surface is improved.