the lower the Qf/Qg value, the higher the extent of interaction between filler and matrix [32]. From the result, it can be seen that addition of ESP caused a reduction in Qf/Qg value. This explains that good rubber–filler interaction could be achieved even at a very high ESP loading. Hence, stronger interfacial adhesion between the filler and the polymer chain was obtained. This result further supports the continuous improvement of tensile strength, M100, compression strength, and hardness up to 10 phr of ESP loading.