Compositions for preparing fire retardant polyvinyl chloride films characterized by their unusual combination of low flame spread, low smoke density, reduced permeability for vapor transmission and good cold crack resistance are described. These film forming compositions comprise a blend of about 40-55% polyvinyl chloride, about 7-20% of chlorinated polyethylene, about 4-20% of a phosphate ester plasticizer, about 3-7% of a magnesium hydroxide filler, about 3-6% of zinc borate and about 3-6% of an antimony trioxide fire retardant with various lubricants, pigments and stabilizers being included where desired. The films derived from the above blend enjoy particular utility in preparing vapor barrier constructions for use in the building trade.