Quantachrome Instruments is a world leader in providing analytical instruments for the characterization of porous materials. One such instrument is the POROMETER 3G series of capillary flow porometers. These instruments utilize the technique known as liquid expulsion to measure the "Bubble Point", pore size distribution of through-pores, and permeability characteristics of membranes and other filtration media.
This is done by applying an ever increasing pressure gradient across a sample wetted with a known fluid and monitoring the resulting flow associated with the emptying of these pores. There is a well-known relationship between the size of a pore and the pressure at which the wetting fluid is expelled (largest through-pore first, then smaller ones). Additionally, permeability measurements are performed by monitoring either gas or liquid flow through the membrane. Results may be presented in a wide range of units including, amongst a long list of options, Darcys, and Gurley and Frazier numbers.