The electrical conductivity values that come into the potential equation are the actual values specific to the used solid or porous materials. The specified values include the fact that some of the used materials such as GDL and MPL are porous. In other words, the porosity does not find its way into the definition of the effective conductivity and into the potential equation explicitly. The conductivity of the the porous materials that are being used in fuel cells is considerably lower than the conductivity values for metals. Please note, the porosity of the material has a pronounced effect on the species diffusion, heat transfer and on the liquid water transport in PEMFC. Keywords: PEM, PEMFC, fuel cells, porosity, conductivity.