The hydrogenated nitrile butadiene rubber (HNBR) based thermal protection systems (TPS) were successfully developed using silica phenolic and carbon phenolic as fillers by filler particle size variation and fixing filler amount in different formulations. Both the TPS were characterized for their confirmations and functional properties using various analytical techniques. The fabricated composites demonstrated improved mechanical, thermal and ablative properties that can meet requirements of aerospace industry for specific applications. A comparative study was also carried out to perceive the effects of particle size of the filler on thermo-mechanical and ablative properties showing that with decrease of the particle size of the filler, mechanical properties and thermal stability increased, while ablation rate decreased. Furthermore, silica phenolic based composites had better mechanical, thermal and ablative properties as compared to its counterpart carbon phenolic TPS. © Published under licence by IOP Publishing Ltd.