In order to further improve the thermal insulation performance of ethylene- propylene- diene monomer (EPDM) based insulators, different virgin layer structures (unfoamed layer, foamed layer and alternating foamed multi-layer) with the same thickness were introduced to the back-face of EPDM-based insulators, and the effects of different virgin layer structures on the thermal insulation performance of EPDM- based insulators were analyzed. Compared with the traditional EPDM- based insulator, the thermal conductivity of EPDM- based insulators is decreased with different degrees as the introduction of the virgin layer structure. The back- face temperature of the samples with alternating foam multilayer structure decreases to a great extent, and the back-face temperature of 8-layer and 16-layer samples is decreased by 14.7 ℃ and 23 ℃, respectively. Compared with the foamed layer structure, the introduction of the unfoamed layer can act as support layer to protect the foamed layer in the alternating foam multilayer structure, so that the foamed structure will not be extruded and deformed when it is subjected to high pressure impact during the ablation, thus giving full play to its thermal insulation advantages.