Expandable graphite (EG), dimethyl methylphosphonate (DMMP), melamine (MEL), zinc borate (ZB), or magnesium hydroxide (MH) was separately added to polyurethane to form flame retardant flexible polyurethane foam (FPUF) in one-step. The cell morphologies of the FPUF composites before and after burning were observed by scanning electron microscopy (SEM), their flammability was evaluated by limiting oxygen index (LOI) tests, and their thermal stability and evolved gaseous products were examined by thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR). The results indicated that all the five flame retardants could improve the flame retardant performance of FPUF on the basis of their own mechanism. DMMP possessed the highest flame retardant efficiency, and one of the important reasons was that it could promote the formation of char. EG could inhibit molten drop of FPUF during burning effectively. All the five flame retardants could decrease the maximum decomposition velocity mainly because of their heat absorption effect. ZB displayed an excellent inhibition ability for the release of the evolved gaseous products because of its adsorption effect. All the flame retardants except DMMP were capable to decrease the CO yield at the temperature (400 degrees C) of maximum decomposition velocity for their respective mechanisms, but all of them were not able to inhibit CO generation at higher temperature (600 degrees C). (C) 2013 Society of Plastics Engineers