Epoxidized natural rubber (ENR) is also higher polar than virgin NR due to the epoxide groups in its structure. The chemical and physical properties of ENR change according to the epoxide contents, such as heat and swelling resistances [12]. By its polar functional groups, ENR interacts with hydroxyl groups on the silica surfaces [13]. It has been reported already that the mechanical properties of silica-filled ENR without coupling agent are higher than those of silica-filled virgin NR [14] and [15].