Cortland Fly Line Backing, MICRON, 20 lb Test, BLUE - 100, 150, 200, 250, 300, 400, 600 up to 2,500 yd Cortland Micron is the standard by which all fly line backing has been judged for over 50 years. World-famous for its tight, round braid, smooth low-friction finish, and stretch-resistant performance, Micron is manufactured from premium Dacron fibers in our New York facility. Unlike looser, flat braids, Micron comes with zero twist, is virtually tangle-free and knots perfectly every time. Various lengths available wound from bulk spools of Cortland Micron Backing You only have to buy what you need - enough to fill one reel or buy in bulk.