A method of producing a polymer polyol dispersion, the method comprising: providing at least one reaction system, the reaction system comprising: a) at least one polyol; b) from 0.5 wt.% to 2 wt.%, based on a total weight of the reaction system, of at least one phosphorus based flame retardant having at least one active hydrogen attached to a nitrogen or oxygen atom; said the at least one phosphorus based flame retardant comprising the reaction product of a reaction mixture, the reaction mixture comprising: at least one polyol; and at least one phosphorus containing compound having the general formula, or combination thereof: wherein X is a leaving group, R 1 and R 2 are, independently of one another, a C 1 -C 8 -alkyl, C 1 -C 4 -alkoxyethyl, C 1 -C 4 -alkyl-substituted C 6 -C 10 -aryl radical, alkyl substituted aryl, aryl substituted alkyl, nitro alkyl, hydroxyl alkyl, alkoxy alkyl, hydroxyl alkoxyalkyl, or R 1 and R 2 together form R in a six-membered ring, wherein the six membered ring has the general formula,, or combination thereof: wherein R is a linear or branched divalent alkylene group containing from 3 to about 9 carbon atoms; c) from 3 wt.% to 15 wt.%, based on the total weight of the reaction system, of at least one amine co-reactant having an equivalent weight of up to 400; d) at least one catalyst; and e) at least one polyisocyanate. a) at least one polyol; b) from 0.5 wt.% to 2 wt.%, based on a total weight of the reaction system, of at least one phosphorus based flame retardant having at least one active hydrogen attached to a nitrogen or oxygen atom; said the at least one phosphorus based flame retardant comprising the reaction product of a reaction mixture, the reaction mixture comprising: at least one polyol; and at least one phosphorus containing compound having the general formula, or combination thereof: wherein X is a leaving group, R 1 and R 2 are, independently of one another, a C 1 -C 8 -alkyl, C 1 -C 4 -alkoxyethyl, C 1 -C 4 -alkyl-substituted C 6 -C 10 -aryl radical, alkyl substituted aryl, aryl substituted alkyl, nitro alkyl, hydroxyl alkyl, alkoxy alkyl, hydroxyl alkoxyalkyl, or R 1 and R 2 together form R in a six-membered ring, wherein the six membered ring has the general formula,, or combination thereof: wherein R is a linear or branched divalent alkylene group containing from 3 to about 9 carbon atoms; at least one polyol; and at least one phosphorus containing compound having the general formula, or combination thereof: wherein X is a leaving group, R 1 and R 2 are, independently of one another, a C 1 -C 8 -alkyl, C 1 -C 4 -alkoxyethyl, C 1 -C 4 -alkyl-substituted C 6 -C 10 -aryl radical, alkyl substituted aryl, aryl substituted alkyl, nitro alkyl, hydroxyl alkyl, alkoxy alkyl, hydroxyl alkoxyalkyl, or R 1 and R 2 together form R in a six-membered ring, wherein the six membered ring has the general formula,, or combination thereof: wherein R is a linear or branched divalent alkylene group containing from 3 to about 9 carbon atoms; c) from 3 wt.% to 15 wt.%, based on the total weight of the reaction system, of at least one amine co-reactant having an equivalent weight of up to 400; d) at least one catalyst; and e) at least one polyisocyanate.