The present invention relates to a reactive formulation used to make a flame resistant flexible polyurethane foam which is particularly suited for use in under the hood vehicle applications. In particular, the flame resistant flexible polyurethane foam is made from a reactive formulation comprising an A side comprising (i) an organic isocyanate and a B side comprising (ii) an isocyanate-reactive component, (iii) a flame retardant component comprising a combination of red phosphorus, expandable graphite, and optionally sodium citrate wherein the resulting foam achieves a V-0 rating at 0.5 inch according to Underwriters' Laboratories Standard 94 Flammability Test.