Capillary flow porometry, also known as porometry, is a characterization technique based on the displacement of a wetting liquid from the sample pores by applying a gas at increasing pressure. It is widely used to measure minimum, maximum (or first bubble point) and mean flow pore sizes, and pore size distribution of the through pores in membranes  nonwovens, paper, filtration and ultrafiltration media, hollow fibers, ceramics, etc.
In capillary flow porometry an inert gas is used to displace a liquid, which is in the pores. The pressure required to empty the pore corresponds to the pressure necessary to evacuate the liquid from the most constricted part of the pore. This most constricted part is the most challenging one and it offers the highest resistance to remove the wetting liquid. This parameter is very relevant in filtration and similar applications since it is important to know the smallest diameter of the through pores.