The document discusses ion exchange membranes and their ionic resistance and permselectivity. It examines how varying properties of the membranes like water uptake, ion content, and surface structure impact resistance and permselectivity. The goal is to design membranes that can be used effectively in reverse electrodialysis to harvest energy from salinity gradients by having low resistance and high permselectivity. Testing of commercial and experimental membranes showed that as water uptake increased, resistance also increased, and resistance generally decreased with higher salt concentrations. Anion exchange membranes tended to have higher resistance than cation exchange membranes.