The basic principle of pore size measurements is that liquid filled pores will become gas permeable at a certain gas flow pressure. This initial differential pressure indicates the bubble point of a material.

As real materials contain a range of pore sizes, the bubble point corresponds to the opening pressure of the largest pore. The measured pressure value is dependent on the surface tension of the test fluid used.

By further increasing the gas flow rate, and therefore the pressure drop across the material under test, it is possible to calculate a pore size distribution from these two measured parameters.

The applied measuring principle is in close accordance with ASTM E 1294-89 and ASTM F 316-03 standards. In addition to test liquid Topor, measurements can be carried out with a range of other test liquids. To achieve reliable results the surface tension of the test fluid must be known and a sufficient wetting of the test sample has to be guaranteed.