Two Gas Diffusion Layers (GDL) further improve the efficiency of the system by allowing direct and uniform mass transfer access of the fuel and oxidant to the catalyst layer, and mechanical support to the membrane. In addition to distributing the gases, the anode GDL also conducts the electrons away from the anode. Then the electrons go back to the anode bipolar plate and current collector. The cathode GDL conducts the electrons to the cathode catalyst layer from the cathode bipolar plate and the current collector, ensuring the complete flow of electrons. Typically, porous carbon paper or cloth is the material used for GDLs.