A composition is disclosed that comprises an otherwise flammable flexible polyurethane foam and a multi-component flame retardant additive. The flame retardant additive includes an alkyl substituted aryl phosphate and an alkyl phosphate ester wherein the alkyl groups range from C4 to C20 and contain one to six oxygen atoms in the alkyl chain. Optionally, the flame retardant additive includes a halogenated flame retardant containing more than 30 wt. percent of bromine, chlorine, or a mixture thereof.