Unsaturated polyester resin is prepared from diethylene glycol and maleic anhydride and can be cross-linked with styrene. It is used as a matrix material for fiber reinforced composites. The document discusses the preparation of unsaturated polyester resin and its composites with nano silica, glass fibers, and bagasse fibers. It is found that adding these fillers improves the mechanical, electrical and thermal properties of the composites compared to neat resin. Nano silica composites in particular exhibit better electrical properties than micro silica or neat resin composites.