Backing is a filler that is installed between your fly line and the reel. Often times in fly fishing you may need more line than a typical 100' fly line allows. Especially when pursuing larger species. The amount of backing can vary from 50 yards for small trout up to 400 yards or more on large saltwater reels. Backing for trout sized fish is often 20# dacron. Backing for saltwater species is often rated up to 68#. If you add backing, a fly line, and reel to your cart our team will properly install it for you at no extra charge. Be sure to confirm with us which hand you plan to reel with (left or right) as it matters what direction the backing and line are wound around the spool.