3M Sanding Sponges, and I discovered a flaw in their system. You can see the three grades: Microfine, Ultrafine, and Superfine. Okay... so which is roughest and which is finest? Those three words have no default relation to each other, so the labels become useless. Adding a number to the label would help, which I did later with a Sharpie - and for the record, from roughest to finest (according to their website) it's Super, then Ultra, then Micro. Now I'm just waiting for them to develop an even finer grade - which they'll call Super-Micro? Ultra-Micro? Super-Duper-Ultra-Micro??