Ethylene–propylene–diene monomer (EPDM) composites were usually enhanced with ablative additives to protect solid rocket motor (SRMs) casings. However, the poor thermal insulation caused by the high thermal conductive ablative fillers can lead to rocket motor failure. Herein, the novel EPDM composites containing alternating layers of ablative EPDM (AM) and heat-insulated EPDM (HM) were prepared through layer-multiplying extrusion. Compared with conventional EPDM ablative material, the multilayer composites showed enhanced thermal insulation and mechanical properties that could be further improved by tuning the number of layers. The ablation and thermal insulation properties possessing in AM and HM layers could be combined by forced assembly during co-extrusion, and the alternating multilayer composite was capable of showing the effect of each component. In particular, compared with AM, the maximum back-face temperature with 40 alternating layers of AM/HM decreased from 96.2 °C to 75.6 °C during oxyacetylene test, while the good ablation properties were preserved in the AM component. This significant improvement was attributed to the planar orientation and densification of ablative additives, and the interruption of conductive pathways in the through-plane direction of AM/HM alternating laminate. The anisotropic EPDM composites featuring mechanical robustness, good ablative resistance and thermal insulation suggest considerable potential application in the aerospace industry.

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.