PURPOSE: To provide an insulating material for covering the molten steel at low cost by constituting the insulating material for coating the molten steel with the incineration residue of wasted building materials or the like as main raw material.

CONSTITUTION: The insulating material for coating the molten steel is constituted with the incineration residue of wasted building materials and/or the garbage as the main raw material. The insulating material is constituted by adding, by weight, 50-90% of the incineration residue of the wasted building materials and/or the life-oriented garbages, 0.5-15% of the binding material, 0.5-3.0% of the thermally expanding material and silica sand as required to form particles or lumps. The wasted building materials are waste paper, wooden chips and/or wooden pieces. Phenol resin and starch are added as the binding material, and the acidificated graphite is added as the thermally expanding material respectively. This constitution prevents the difficulties such as the cooling and oxidation of the molten steel surface by covering the molten steel surface to separate the molten steel surface from the atmosphere.