[en] Improving flame retardancy is one of the most crucial issues to use polymeric materials for building construction. Most of the flame retardant materials containing halogen atoms delay fire spread, but produce harmful gases during combustion. Hence, we designed and fabricated a composite foam by using a green nanomaterial. Silylated and nanofibrillated cellulose (Si-NFC) was added to polyurethane foam (PUF) containing tris(2-chloropropyl) phosphate (TCPP) in order to reduce the emission of smoke during combustion. Thermal characteristics of the composite foams were investigated through thermogravimetric analysis, limiting oxygen index (LOI), and cone calorimeter tests. The LOI of the Si- NFC embedded composite was increased from 19.3 % to 24.6 %. In addition, the Si-NFC led to an improvement in the thermal stability of the composites by reducing the peak release of heat and smoke. Chemical structure of the residual char was analyzed by using energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy.