At instantaneous thermal shocks and high temperature conditions, using the charring ablative heat shields is more effective than the other heat protection methods. In recent years, low-filled layered silicate polymeric nanocomposites were introduced as new class of ablative materials. In this work, highly filled ablative polymeric nanocomposite is prepared and its thermal stability and ablation mechanism is studied under high external heat flux. The thermal degradation kinetics during pyrolysis, the variation of thermophysical properties as a result of ablation process and mathematical modeling of ablation process are performed for highly filled ablative polymeric nanocomposite samples compared with those of their composite counterparts under oxyacetylene flame test. The results show that the ablation performance of highly filled polymeric nanocomposite is higher than that of the composite, and the mathematical model is adequately confirmed by the experimental data of the thermophysical and ablation properties of highly filled nanocomposites. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2776-2785, 2013