Cortland Micron Backing 20lb, Cortland Micron is the standard by which all fly line backing has been judged for more than 50 years. World famous for its tight, round braid, smooth low-friction finish and stretch-resistant performance, Micron is manufactured from premium Dacron fibers. Unlike looser, flat braids, Micron comes with zero twist, is virtually tangle-free and knots perfectly every time. Ask any fly angler who sees their backing more than most, and they’ll tell you they use Micron — all the time. 20-lb. test.