Essentially the main difference between the 3×3″ Sponge Electrodes and the 2×2″ Sponge Electrodes is the size of the electrode pad and the area they cover. They both are constructed in exactly the same way, with the same materials and use the same Amrex electrode cables and adapters. The 3×3″ electrodes will cover a broader area, while the 2×2″ will cover a slightly smaller, more condensed area. Essentially the 2×2″ sponge electrodes will stimulate a more targeted area, while the 3×3″ have more of a generalized effect on the area being stimulated. Additionally, because of the larger surface area, the 3×3″ size generally provides a more comfortable session with fewer negative side effects. Due to these facts, the 3×3″ size sponge electrodes are far more popular than their 2×2″ counterpart.