Both the original Fuel Cell and Electrolysis module as well as the new PEMFC module allow a user to specify contact resistivities at the joints between solid current collectors and/or porous gas diffusion and catalyst layers. Typically, there is one physical location where a user might want to specify the actual resistivity value. However, there are a couple of entitites such as a wall and a wall-shadow that exist in this location and the contact resistivity can be specified at both. Please note that the values specified at the adjacent wall and wall-shadow will be summed up. It is a good practice, to specify the contact resistivity only on one single entity. Please also note that the wall and wall-shadow entities exist on the boundary between the solid and the fluid (porous) regions. There might be a need to prescribe the contact resistivity between two porous fluid regions, for example between the gas-diffusion layer and the catalyst layer. In such cases, there is only one entity in between these regions. By default the interface type is internal. Please note that the contact resistivity cannot be applied to the internal interface type. One can specify the value in the GUI, but it will not become effective until the interal interface type is changed to the porous jump. The bottom line is that the contact resistivity can only be specified at either walls or wall-shadows or at porous-jump types of interfaces. All other entries to different interface types are ignored by the solver.