Click any image to enlarge

Product Description:
Backing is what connects your fly line to the reel, and gives you that extra length when a big fish takes off with your fly! When you look at a fly reel (by the way, our come pre-loaded with backing...) the majority of what you see is backing, not fly line. A common mistake to make!
 
Remember, the backing doesn't have to float, or "perform" like the fly line does, so this is really just a safety against fish that run longer than about 150 feet, and believe me, they do!