AbstractThe gas diffusion layer (GDL) of the proton exchange membrane (PEM) fuel cell is a vital component in water management since humidification and water removal are both achieved through the GDL. Capillary action in the GDL porous structure enhances water removal from the cathode catalyst layer, and hence prevents flooding which blocks the pathways of the reactants to the activation sites. To improve the transport of water and reactants, GDL properties are varied by changing the geometry and the PTFE loading of the carbon fiber paper (CFP), both changing the internal wettability of the GDL. In essence, the wettability describes the interaction of water with the porous structures inside the GDL. The knowledge of the surface properties and pore structure is important to enhance water management in the cell. In this work, two ex-situ techniques are used to measure transport characteristics of GDLs, such as the internal wettability, pore size distribution and permeability. These measurements have been applied to different types of GDLs with different structures and PTFE loadings. The comparison between the results will determine the effect of material and treatment on the properties of GDLs which can provide basic insight into the two-phase flow in this porous layer.