The new Ultrafine Volcanic Bag (Patent Pending) with cleat is 75 microns. It has a no-lead design and is tested to pick up most fire ash and DE powder. Use this bag for special cleanup and when the pool is mostly clean. (Tag Color: White.) ABOUT OUR BAGS: Authentic HammerHead debris bags are hand made here in the USA and are inspected prior to packaging and shipment. Each bag has a tag with the HammerHead name that indicates what type it is. We warranty them against defects in workmanship but not against wear and tear. Treat your debris bags with care. Dragging them on the bottom of the pool, the deck, or across the coping when lifting them out of the water can wear holes in them. Empty them frequently while vacuuming, and store them clean, dry, and out of the sunlight for the longest life. ABOUT BAG SIZE: XL bags are approximately two times the capacity of our normal bag and measure about 48" in length. A normal standard, superfine or coarse bag is about 24". ABOUT MICRON RATINGS: A micron is one millionth of a meter, or approximately .00003937 inches. The smaller the micron number, the finer the bag. As debris goes, anything below about 40 microns is smaller than the human eye can easily see. White blood cells are about 25 microns, red blood cells are 8 and bacteria generally around 2 microns.