18"x30" Vacuum/Xtra Polishing Bag™ Your water passes through the sand filter which traps particles at about 50 microns. Then the water is polished by the SlimeBag™ to about 1 micron which removes fine particulate matter.. Just to give you an idea of how small that is, a grain of sand is about 100 microns 1 micron is smaller than a red blood cell.