For most compounds, the elongation at break showed an upward movement as did the compression set. However, this was not the case for Compounds 2 and 3, 12 and 13, and 17 and 18 (Table IV). Since higher compression set was due to lower CLD (Tables IV), this also explained the higher elongation at break because as CLD decreased, the rubber chains were less restricted and could stretch more when load was applied to the rubber. The compression set and rubber hardness did not correlate in an obvious way. For some compounds, e.g. Compounds 2–4, the compression set increased by 113%, whereas the hardness reduced only by 1.3%. For the carbon black-filled compounds, the hardness remained between 71 and 80 Shore A whilst the compression set changed from 5.5 to 37.4% (Table IV). The silica-filled compounds were the hardest at 80–85 Shore A. As stated earlier, the silica-filled compounds had higher crosslink densities because of the reaction of the tetrasulfide groups of TESPT with the rubber chains, which produced additional crosslinks in the rubber. Previous studies showed no obvious correlation between compression set and mechanical properties such as hardness, tear strength, resilience, and abrasion loss.35 Our results seemed to confirm these earlier findings