Flexible and porous epoxidised natural rubber (ENR)/polyvinyl chloride (PVC) membranes were prepared via phase inversion technique. The pore formation on ENR/PVC membranes was initiated with the introduction of inorganic particles (silica). Two types of silica, microsilica (microcrystalline silica powder) and nanosilica [generated from Tetraethoxysilane (TEOS)] were used. Effects of silica addition on the membrane structure are investigated by means of FTIR, SEM, TGA, and UTM. FTIR results showed the presence of signature peak of SiOSi at 1102 and 1088 cm-1 for ENR/PVC/SiO2 and ENR/PVC/TEOS membrane, respectively. Morphological studies showed that pores developed in ENR/PVC/TEOS membranes were more homogenous as compared to ENR/PVC/SiO2 membranes. Thermal and mechanical stability of the membranes improved with the incorporation of silica. ENR/PVC/SiO2 membrane exhibited better mechanical and thermal properties as compared to ENR/PVC/TEOS membranes. CO2 and N2 gas permeation of silica-filled membranes increased with increasing silica content and the permeability of ENR/PVC/SiO2 membrane toward N2 and CO2 gasses was higher than ENR/PVC/TEOS membrane. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013