Thick vs Thin Sponge for Soldering
The sponge comes thin as purchased because the cells have been flattened, but once it is wet the cells relax and the sponge will take its final form. There is no difference between thicknesses of sponge as all they are doing is abrading off the solder without damaging the tip. The grooves provide a larger abrasion surface without increasing the volume of the sponge.