Abstract: Herein disclosed is a filter medium for molten metals which consists of a sintered body of a mixture comprising 100 parts by weight of at least one refractory grain selected from the group consisting of alumina particles and Al.sub.2 O.sub.3.MgO spinel crystal particles; and 5 to 25 parts by weight of an inorganic binder which comprises 60 to 90% by weight of Al.sub.2 O.sub.3.MgO spinel crystal powder, 5 to 12% by weight of B.sub.2 O.sub.3, and not more than 30% by weight of at least one oxide selected from the group consisting of Al.sub.2 O.sub.3, MgO and TiO.sub.2. The filter medium is used for filtering off solid impurities mixed in molten metals, in particular, molten aluminums.

Abstract: A filter medium which permits an increased amount of filtration. The filter medium can be prepared by blending 100 parts by weight of aggregate particles, 5-18 parts by weight of an inorganic bonding material having a chemical composition of about 10-50% by weight of SiO.sub.2 and about 5-20% by weight of B.sub.2 O.sub.3 and containing at least 70% by weight of a non-vitreous substance such as talc or boric acid, and about 3-15 parts by weight of a combustible substance such as wheat flour, kneading the mixture with a caking material and water, molding the kneaded mixture, drying it, and then calcining the dried mixture at a temperature not lower than about 1100.degree.C. The size and number of the air-permeable pores in the filter medium can be controlled by adjusting the amounts of the bonding material and combustible substance.