Electrospun nanofibrous webs are important in nanotechnology applications due to their high surface area and interconnected porosity. In this study, the effect of electrospinning duration on some physical and mechanical properties of polyurethane (PU) electrospun webs is investigated for potential applications such as protective clothing and membranes. The results show that the thickness and weight of webs and subsequently their tensile strength increase linearly with the electrospinning duration. Air permeability of nanofibrous webs decrease and hydrostatic pressure increases nonlinearly while water vapor permeability remains constant. This work shows that air permeability of PU webs follows Fick's law of diffusion. Some regression models have been proposed to describe electrospun membranes behavior. The results of this investigation indicate that this new generation of nanofibrous materials has a good potential for application as membrane in protective clothing. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012