Fig. 5 shows the swelling of gum vulcanizates and NR vulcanizates filled with OPA, silica and carbon black. It wasclearly observed that swelling reduced when 50 phr carbon black was added compared to 10 phr silica and 1 phr OPA.This is mainly due to the increased amount of filler loading.The OPA, silica and carbon black could act as a barrier to restrict the toluene solvent from penetrating into NR vulcanizates.The amount of toluene uptake can be affected by various factors such as filler loading, types of elastomer,crosslink types and density [12]. However, the main factor here seems to be the filler loading.