For best results, we recommend you replace your sponges every two weeks, or after 7 tDCS sessions. However the best results can be obtained by using new sponges for each session. Replacement sponges can be found in packs of 10 in our online store. Over time, the sponges within Amrex rubber electrodes can grow brittle and crumble, crack, or split, causing an uneven distribution of current. Worn-out sponges can cause an uncomfortable tDCS session, with increased tingling, itching, and sometimes stinging sensations occurring. A good way to tell if your sponges need replacing is if soaking them with saline solution becomes more difficult, if they start to display a darker/brownish color, or begin feeling “stale.” More importantly, if your tDCS sessions become uncomfortable, or you start to notice sensations that maybe you didn’t before, this is a good sign that your sponges need replacing. You can find 10-packs of replacement sponge inserts for both the 3×3″ Amrex Electrodes and the 2×2″ Amrex Electrodes through our online store.