Nanofibrous composite membranes were prepared by the elecrospinning process of poly(vinyl butyral) (PVB) solution that contained hydrophobic silica nanoparticles (SiO2). Various surface modifications of the silica nanoparticles have been used to improve the waterproofing capacity of the membrane. Specifically, investigation was made into the effects of the rheological properties of the solution, as well as on fibre diameter as exerted by the applied voltage and the tip-to-collector distance. It was found that drastically increasing shear viscosity and the elasticity of the solution with the silica nanoparticles demonstrated a negligible effect on the creation of nanofibres, an issue rarely discussed in the literature. In fact, increasing the applied voltage and the tip-to-collector distance resulted in heightening the average fibre diameter. According to water contact angle measurements, the given PVB nanofibrous membrane reinforced with the incorporated silica nanoparticles demonstrated superhydrophobic surface properties.