The hydraulic permeabilitics of electrospun fiber mats are found to be functions of their compressibility. Hydraulic permeabilities of electrospun mats of bis-phenol A polysulfone (PSU) comprising fibers of different mean diameters, annealed at temperatures at and above the glass transition of the polymer, were measured for feed water pressures ranging from 5 kPa to 140 kPa. The electrospun mats experience a decrease of more than 60% in permeability between 5 kPa and 140 kPa, due to the loss of porosity, attributed to flow-induced compression. This behavior is explained using a simple model based On Darcy's law applied to a compressible, porous medium. Flappers equation is used to model the permeability of the fiber mats, and Toll's equation is used to model their compressibility. The permeation model accurately estimates the changes in solidity, and hence the permeability of the electrospun mats, over a range of pressure differentials. (C) 2013 Elsevier B.V. All rights reserved.