In order to better understand the two phase properties of the porous GDL, the liquid water pattern and local saturation in the Toray 060 gas diffusion layer (GDL) is visualized in-situ in cells close to the optimal performance point at 80°C by X-ray tomographic microscopy. A recording time of about 10 s is achieved. At the optimal performance point (dew point of reactant gases 74 °C) the water volume fraction observed depends on the rib width. A variation of ± 8 °C of the feed gas dew point leads to significant saturation and performance changes. For different current densities the water volume fraction and permeability of the liquid phase of the cathode are determined and analyzed.