Researchers developed bio-based polyurethane (BPU) using a castor oil/poly (ε-caprolactone) hybrid polyols and hydrophobic BPU ultrafine fibres containing modified silica (m-silica) by electrospinning process. The rheological analysis of the network structure between the BPU and m-silica showed improved mechanical properties and thermal stability. The average fibre diameter of the hybrid ultrafine fibres decreased with increasing m-silica content. Moreover, the m-silica nanoparticle provided an effective surface wettability to BPU ultrafine fibres, thus making it a hydrophobic molecule. All these improved properties makes BPU/m-silica ultrafine fibres, a better replacement for petroleum-based polyurethane membrane, thus allowing its application in the field of bio filters, eco-friendly textiles, and biomedical engineering.