A method for determining pore structure characteristics of hydrophobic porous materials includes placing a test sample of material in the sample chamber of a porosimetry apparatus, creating a partial vacuum and evacuating the sample chamber to remove air, creating a partial vacuum and evacuating the penetrometer and storage vessel above the water level, releasing the vacuum in a controlled manner, so pressure is applied and water in the penetrometer enters the sample chamber and intrudes into pores of the sample, applying a measured amount of intrusion pressure and measuring the change in volume of water in the penetrometer, and determining pore structure characteristics of the sample based on the change in volume of water in the penetrometer. The method further includes an optional step of applying a desired amount of compressive stress on the sample prior to testing. Nonporous plates optionally are used to measure x-y plane pore structure.