In this paper the influence of micro-sized (3 $\mu $m) and nano-sized (10 nm) silica (SiO$_{2})$ on mechanical, thermal, and electrical properties of silicon rubber (SiR), epoxy, and ethylene propylene diene monomer (EPDM) composites is presented. The micro- and nano-sized SiO$_{2}$ particle-filled SiR, epoxy, and EPDM composites were formulated with 20% microsilica and 5% nanosilica by weight respectively. Among these composites, SiR-SiO$_{2}$ amalgamation was performed by mixing using an ultrasonication procedure. Epoxy-SiO$_{2}$ was compounded in two steps, i.e. dispersion of fillers and mixing, whereas EPDM-SiO$_{2}$ compounding was performed with a two roll mill technique. With the addition of micro/nano-SiO$_{2}$, the composites showed enhanced tensile strength of $\sim $2.7 MPa, improved hardness, and reduced elongation at break. Further incorporation of micro/nano-sized particles resulted in high thermal stability for SiR-nano composites (SNCs) as compared to epoxy and EPDM composites. Compared to SiR and EPDM composites, epoxy-nano composites showed the highest value of dielectric strength, i.e. 38.8 kV/mm. Meanwhile, the volume and surface resistivity of SNCs were found higher as compared to other investigated samples. Promising properties of SiR nanocomposites among all the investigated samples suggest that their application is more suitable for utilization in outdoor electrical insulations.