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 {HEAD ~ an entire thickness} of a test sample and a second stream of fluid applied across an entire thickness of {TAIL ~ a reference sample} 
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 { HEAD ~ an entire thickness } of a test sample and a second stream of fluid applied across an entire thickness of { TAIL ~ a reference sample }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL