PURPOSE: The titled composition having extremely improved heat distortion resistance and processing characteristics without damaging characteristics of the resin of its own, by blending a vinyl chloride resin with a specific methyl methacrylate polymer.

CONSTITUTION: At least 40W95pts.wt. vinyl chloride polymer comprising at least 80wt% vinyl chloride is blended with 60W5pts.wt. at least one methyl methacrylate polymer having 0.005W0.2l/g, preferably 0.3W0.06l/g reduced viscosity, comprising at least 75wt% methyl methacrylate. Ethyl acrylate or butyl acrylate is preferably as a copolymerizable monomer for the methyl mechacrylate copolymer.