This work presents an experimental method that is one of the few to allow both imbibition and drainage capillary measurement at pressures above breakthrough. It was used on Toray and SGL Carbon gas diffusion materials at room temperature. These materials exhibited both hydrophobic and hydrophilic properties. Breakthrough pressures for Toray and SGL Carbon were 3.6 and 1.5 kPa, respectively. Little hysteresis was observed in these room-temperature experiments, which is an interesting contrast with the results from the only other group, Schwartz's group at University of Washington, to measure these properties. A double exponential equation was used to fit the data for each carbon paper.