Quantachrome's 3G Porometers employ the method of capillary flow porometry, also known as the liquid expulsion technique, uses the simple principle of gas pressure to force a wetting liquid out of through-pores in a sample. Through pores are simply those that connect from one side of the sample to the other. The pressure at which pores empty is inversely proportional to the pore size, larger pores require a lower pressure than do smaller pores. The resulting volumetric flow of gas through emptied pores is also measured. Pore size is calculated using the Washburn equation.
The largest pore to be emptied (at the lowest pressure at which flow is sensed) defines the so-called "bubble point". After all pores have been emptied (up to the highest pressure achievable) during the "wet" run, a second "dry" run is performed on the same sample. From the complete data set, various flow-related pore size parameters, pore size distributions and gas permeability can be calculated.