A substantially uniform injection moldable foamable blend comprising a 5-phenyl-3,6-dihydro-1,3,4-oradiazin-2-one and thermoplastic organic polymeric material having at least 5% by weight of chemically combined haloalkylene polycarbonate units of the formula, ##STR7## where R5 and R6 are the same or different divalent aromatic radicals having from 6-13 carbon atoms, X is a halogen atom and X1 is s