Abstract: An improved closed cell polymer foam and foaming agent involving the use of a hydrogen-containing halocarbon blowing agent (e.g., HCFC-22) in combination with an effective amount of a hydrogen bond forming blocking agent (e.g., organic ether, ester or ketone). The presence of the blocking agent is shown to significantly reduce the escape of blowing agent from and entry of air into the foam resulting in low thermal conductivity over a longer period of time and improved thermal insulation value. A closed cell thermoplastic foam such as polyethylene, polypropylene, polystyrene, among others, is disclosed produced by means of an environmentally friendly nonflammable blowing agent substantially free of halogen substituents other than fluorine and comprising HFC-134 (1,1,2,2-tetrafluoroethane).