The layer may either be Insulating, Resistive (supporting electrolytes only) or an Ion exchange membrane.

For Resistive or Ion exchange membrane, the potential drop over the membrane is determined either from the Surface resistivity or the Thickness and conductivity.

For Ion exchange membrane, the choice of Charge-carrying species concentration species specifies that the current flowing over the layer will be carried by this species (which must have a non-zero charge number). The potential condition may be either Donnan, which will calculate the potential shift over the boundary based on the membrane charge carrying species concentration, or can be User defined.