Abstract: Permeability of a porous, sheet-like sample is determined using a device that is designed to measure the pressure differential between a first stream of fluid applied across an entire thickness of a test sample and a second stream of fluid applied across an entire thickness of a reference sample. The flow rate for both the test fluid flow system and the reference fluid flow system is determined independently, by measuring a pressure drop throughout the flow system. Data obtained from pressure and flow rate for test and reference fluids are used to calculate percent change in permeability and/or actual permeability using Darcy's Law.