Typically a braided dacron line that connects the reel’s spool to the fly line. This also fills up the spool before the fly line is attached (see spool and nail knot). On larger and harder fighting fish, the backing becomes important when they decide to make a hard run that runs out all of the fly line since fly lines are typically only 75-105 feet in length.
Clint Losee is an avid fly angler of 30+ years, web developer, and Utah Landscape & Nature Photographer. You can connect with him on Instagram, Facebook, or Twitter. Curious about some of the gear he uses? Check out the new Amazon store.