Experimental results about the impact of hydrophobic coating inside commercial gas diffusion layers (GDL) of polymer electrolyte fuel cells (PEFC) were obtained with four different combinations of PTFE-loadings on both anode and cathode. The measurements were performed on differential PEFCs which were characterized with high resolution neutron radiography (NR) combined with two electrochemical methods: a pulsed gas analysis (PGA) and limiting current density measurements. Using the combination of the neutron radiographs with these two electrochemical measurements, a new insight on the impact of water on mass transport losses was obtained. Under high humidification conditions, GDLs without hydrophobic coating do not accumulate more water than coated GDLs, but the water distributes differently and accumulates in the region under the channel of the flow field. Cells with high PTFE coating show higher mass transport losses despite the relatively small quantity of water, which can be explained by a different morphology of water accumulation.