Foamable thermoplastic resin compositions are provided having vinyl chloride polymer, a graft copolymer having a superstrate grafted to a substrate wherein the superstrate has alphamethyl styrene, unsaturated nitrile, and unsubstituted styrene therein, and the substrate is a butadiene rubber, a rubber-free copolymer having alkylmethacrylate, vinyl aromatic, and unsaturated nitrile therein, and a chemical blowing agent. The foamable thermoplastic resin composition may be coextruded with a non-foamed thermoplastic resin skin to produce a coextruded rigid foamed structure by a process of coextruding the skin and foamable thermoplastic composition. The composition and process are useful for, making coextruded rigid foam structures which are useful in rigid foam applications such as foamed pipe and foamed sheet.