Abstract: A casting resin wherein the finished casting has a combined vinyl resin content of from 20 to 65% prepared by polymerizing monomer, for instance methyl methacrylate in the presence of A) vinyl resin, for instance, polyvinylchloride or polyvinylchloride-polyvinylidene chloride copolymer having a particle size within the range of 0.2 to 5 .mu. and B) vinyl resin, for instance polyvinylchloride or polyvinylchloride-polyvinylidene chloride copolymer having a particle size within the range of 15 to 150 .mu., wherein said monomer is a non-solvent at room temperature for said vinyl resins.