The composite materials of different filler concentration were fabricated by reinforcing the glass fiber and silica nanoparticles into epoxy to understand the variation in surface wettability, water droplet initiated discharge, dielectric parameters, surface charge, space charge and mechanical properties. Nanofiller inclusion has shown the enhanced surface properties viz. water droplet initiated corona inception voltage (CIV) and hydrophobicity. CIV is high under negative DC voltage followed with positive DC and AC voltage. It is realized that the dielectric constant is increased with the addition of nano-silica. The surface potential has decayed exponentially irrespective of the applied voltage polarity and the type of the sample, whereas, the 3 wt% sample showed the highest decay rate for an applied voltage. Silica filled composites have shown better space charge accumulation and decay characteristics initially and then deteriorated rapidly when the filler concentration is increased. The optimised filler concentration is found considering the minimal space chare accumulation, decay rate and the optimised electric field for the space charge analysis. Further, the optimised field conditions were devised for the optimum filler concentration for the prolonged life span and reliability of the insulation material. The mechanical storage modulus has increased with the addition of nanofiller. The plasma temperature calculated from the LIBS spectra has shown a direct correlation with the surface hardness of the material. © 2019 IOP Publishing Ltd.