Thermal properties and flammability behavior of two grades of fire retardant polypropylene and nylon 66, and their base resins were determined. A nylon 6 base polymer and a nano-composite based on that polymer were also analyzed. Thermal gravimetric analysis showed more complex degradation patterns for the fire retardant grades as compared to the base resin. This was attributed to decomposition of ingredients present in the fire retardant. Degradation of polypropylene in air started at about 100°C lower temperature than degradation in nitrogen. For nylon, the degradation in both atmospheres occurred at approximately the same temperature. Modulated Differential Scanning Calorimetry (MDSC) measurements were used to determine melting and glass transition temperatures, heats of fusion, heat capacity and thermal conductivity. Both phosphorus-based and halogen-based fire retardants modified the ignition, propagation, and melt-dripping behavior of nylon and polypropylene during burning. Incorporation of a nano-filler was found to be ineffective in imparting fire retardancy to nylon 6. Performance of these materials will have to be evaluated in actual vehicle applications and fire exposures before use on a broad scale basis.