Abstract: A polymer composition adapted for use in producing polyvinyl halide polymer products comprising a blend of a vinyl halide polymer and a particulate terpolymer having a molecular weight of at least about 100,000 and a glass transition temperature of at least about 50.degree. C. The terpolymer comprises repeating units derived from an olefin, a diester of an addition polymerizable unsaturated dicarboxylic acid, and a solubilizing monomer which promotes compatibility of the terpolymer with the vinyl halide polymer. A shaped plastic article produced from this composition, and method of producing the shaped article are also disclosed.