A reactive formulation for making a flame resistant flexible polyurethane foam comprising a mixture of: an A side comprising (i) one or more organic isocyanate, wherein said organic isocyanate comprises monomeric MDI, polymeric MDI, combinations there of, and/or liquid variants thereof obtained by introducing uretonimine and/or carbodiimide groups forming polyisocyanates, said carbodiimide and/or uretonimine modified polyisocyanates having an NCO value of from 29 to 33 percent and included in said polyisocyanate is from 1 to 45 percent by weight of 2,4'-diphenylmethane diisocyanate in the form of a monomer and/or a carbodiimidization product thereof; and a B side comprising: (ii) one or more isocyanate-reactive component comprising an ethylene-oxide capped polyether polyol, (iii) a flame retardant component comprising a combination of: (iii.a) from 0.1 to 6 parts by weight red phosphorus, (iii.b) from 0.5 to 10 parts by weight expandable graphite, and (iii.c) optionally from 0.5 to 15 parts by weight sodium citrate, wherein the flame retardant component does not contain ammonium polyphosphate and wherein parts by weight are based on the total weight of the B side, and (iv) one or more additional component selected from a catalyst, a blowing agent, a cell opener, a surfactant, a crosslinker, a chain extender, a flame retardant, a filler, a colorant, a pigment, an antistatic agent, reinforcing fibers, an antioxidant, a preservative, or an acid scavenger, wherein said flame resistant flexible polyurethane foam made from the reactive formulation achieves a V-0 rating at 0.5 inch according to Underwriter's Laboratories Standard 94 Flammability Test. an A side comprising (i) one or more organic isocyanate, wherein said organic isocyanate comprises monomeric MDI, polymeric MDI, combinations there of, and/or liquid variants thereof obtained by introducing uretonimine and/or carbodiimide groups forming polyisocyanates, said carbodiimide and/or uretonimine modified polyisocyanates having an NCO value of from 29 to 33 percent and included in said polyisocyanate is from 1 to 45 percent by weight of 2,4'-diphenylmethane diisocyanate in the form of a monomer and/or a carbodiimidization product thereof; and (i) one or more organic isocyanate, wherein said organic isocyanate comprises monomeric MDI, polymeric MDI, combinations there of, and/or liquid variants thereof obtained by introducing uretonimine and/or carbodiimide groups forming polyisocyanates, said carbodiimide and/or uretonimine modified polyisocyanates having an NCO value of from 29 to 33 percent and included in said polyisocyanate is from 1 to 45 percent by weight of 2,4'-diphenylmethane diisocyanate in the form of a monomer and/or a carbodiimidization product thereof; a B side comprising: (ii) one or more isocyanate-reactive component comprising an ethylene-oxide capped polyether polyol, (iii) a flame retardant component comprising a combination of: (iii.a) from 0.1 to 6 parts by weight red phosphorus, (iii.b) from 0.5 to 10 parts by weight expandable graphite, and (iii.c) optionally from 0.5 to 15 parts by weight sodium citrate, wherein the flame retardant component does not contain ammonium polyphosphate and wherein parts by weight are based on the total weight of the B side, and (iv) one or more additional component selected from a catalyst, a blowing agent, a cell opener, a surfactant, a crosslinker, a chain extender, a flame retardant, a filler, a colorant, a pigment, an antistatic agent, reinforcing fibers, an antioxidant, a preservative, or an acid scavenger, (ii) one or more isocyanate-reactive component comprising an ethylene-oxide capped polyether polyol, (iii) a flame retardant component comprising a combination of: (iii.a) from 0.1 to 6 parts by weight red phosphorus, (iii.b) from 0.5 to 10 parts by weight expandable graphite, and (iii.c) optionally from 0.5 to 15 parts by weight sodium citrate, wherein the flame retardant component does not contain ammonium polyphosphate and wherein parts by weight are based on the total weight of the B side, and (iii.a) from 0.1 to 6 parts by weight red phosphorus, (iii.b) from 0.5 to 10 parts by weight expandable graphite, and (iii.c) optionally from 0.5 to 15 parts by weight sodium citrate, (iv) one or more additional component selected from a catalyst, a blowing agent, a cell opener, a surfactant, a crosslinker, a chain extender, a flame retardant, a filler, a colorant, a pigment, an antistatic agent, reinforcing fibers, an antioxidant, a preservative, or an acid scavenger,