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With improvements to the performance of ramjets, the ablation environment in afterburning chambers has become more severe, leading to an urgent demand for high-performance thermal protection materials (TPMs). In this study, the reinforcing effects of silicon carbide (SiC) nanowhiskers and nanopowders on silicone rubber composites and their synergistic effects were investigated. Both SiC nanowhiskers and nanopowders improved the thermal stability of the TPMs. SiC nanowhiskers enhanced the thermal conductivity of the TPMs by forming thermal conductivity pathways. Furthermore, SiC nanofillers can reinforce the ablation resistance of the TPM. The best performance was demonstrated by the TPM formulated with five parts SiC nanowhiskers and five parts SiC nanopowders. The ablation rate was reduced by 72.7% relative to the TPM with a basic formulation, and the back temperature increased by only 27.1%. In this study, the SiC nanofiller improved the ablation resistance of composites by densifying the pore structure and strengthening the skeleton of the char layer. Furthermore, the more compact char layer improved the thermal conductivity of the composites. The increase in the thermal conductivities of the composites and the char layer led to a decrease in the thermal insulation properties of the composites. [ABSTRACT FROM AUTHOR]