a novel epoxy resin composition is prepared by first mixing 100 parts by weight of an epoxy resin having an epoxy equivalent of no more than 200 with 0 . 5 - 10 parts by weight of a phenoxy resin to form a uniform mixture , then blending the mixture with a curing agent and an inorganic filler . the epoxy resin composition has a suitable degree of rigidity and softness within the molecular chain without sacrificing its resistance to heat or thermal shock and will not cause precipitation of any portion of the filler in the resin composition . this resin composition is useful in the making of cast insulators employed in electric machines .