Expandable graphite (EG) and dimethyl methylphosphonate (DMMP) were added to polyurethane to form flame-retardant high-resilience flexible polyurethane foam (FPUF) in one-step. The effects of EG and DMMP on cell morphology, mechanical properties, dynamic mechanical properties, thermal degradation, and flame-retardant properties of FPUF were studied. The results indicated that adding proper amount EG or/and DMMP would not seriously damage cell morphology and mechanical properties. Dynamic mechanical analysis (DMA) demonstrated that there were two tan d peaks attributed to soft and hard segment seperately and 15 pbw EG or/and 15 pbw DMMP could enhance damping property of FPUF. Thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR) results indicated that 15 pbw EG or 15 pbw DMMP could improve the thermal stability of the second degradation step but there were no synergistic effect between the two. DMMP made FPUF composites produce more toxic gases such as CO, however, EG displayed an opposite effect. Both EG and DMMP could effectively improve the flame retardant properties of FPUF, and there was synergistic effect between the two. (C) 2013 Wiley Periodicals,