Backing serves several purposes. A big fish is going to run quickly and pull all of your fly line from the spool, and you will then need some extra line to hold them. If you have a big fish on, this is its primary role but it also serves another role, it fills up the dead space on a spool. While not as critical on a large arbor reel, if fly line was wrapped directly around the shaft of an empty spool, it would retain line coils terribly when the diameter of a spool is small. Also the amount of line retrieved per handle rotation would be minimal. By building up the spool with backing, more line is retrieved quickly when winding the reel. BFC Discovery backing is perfect mix between price and quality. Color: White / 50m / 20lb