Polyurethane (PU) is an exclusive class of polymers with special significance in membrane technology. In this work, PU was synthesized using isophorone diisocyanate and polyethylene glycol and possible reaction mechanism and interactions are proposed in an effort to explain the properties of PU as membrane. A series of PU membranes doped with silica nanoparticles (SiNPs) were prepared. The effect of doping of SiNPs (0.01–0.03 wt%) was investigated in terms of structural, thermal, morphological, contact angle, mechanical, antibacterial and permeation properties of the prepared membranes. The FTIR band at 944 cm⁻¹ confirmed the impregnation of SiNPs in PU matrix. The contact angle measurements revealed improved hydrophilic character of silica-doped membranes as compared to pure PU membrane. The SEM analyses exposed a uniform dispersion of SiNPs in PU matrix up to 0.02%, while aggregation was perceived at higher content. The PU membranes with the highest SiNPs content (0.03%) showed the highest thermal stability and tensile strength. The systematic study of desalination demonstrated the RO capability of prepared membranes. The membrane with 0.02% loading of SiNPs supported for highest salt rejection (92.5%) and water flux (22.8 L/h m²) at effective pressure of 20 bar. Hence, these results recommend the PU membrane doped with 0.02% SiNPs as a promising candidate for reverse osmosis applications.