The POROMETERS 3G micro, 3G macro, 3Gz and 3Gzh are latest generation capillary flow porometers. Using the technique known as liquid expulsion, they measure pore size distributions and other related information of through-pores in membranes and other filtration media . In this technique, an increasing pressure is applied to one side of awettedporous sample while pressure and flow rate are monitored. As the pressure is increased, the pores in the sample are progressively emptied (largest through-pore first, then smaller ones). The flow rate through the emptied pores is recorded and used together with the pressure to provide information such as the maximum pore size, the mean flow pore size and full pore size distributions.