In-plane gas permeability measurements were performed on electrospun polyacrilonitrile fibrous mats. Samples were cast onto a drum rotating at various speeds in order to create materials with different degrees of fiber alignment. Permeability measurements were made in both parallel and perpendicular directions and large increases were seen for flow in the fiber direction as expected. Because these measurements were performed in-plane it was necessary to mechanically compress the samples during measurement. Tests were performed at several compressed thicknesses, but it was found that the samples did not compress uniformly so it was not possible to determine a unique Carman-Kozeny constant for the material. A methodology was developed by which the Carman-Kozeny constant was determined for each compression that produced a linear trend against compressed porosity It was proposed that the true Carman-Kozeny constant for the material can be determined by extrapolating this trend to the value of the uncompressed porosity, and good agreement with the literature values was obtained. (C) 2014 Elsevier B.V. All rights reserved.