This high-visibility fluorescent orange flyline backing lets you see the backing in the water when a big fish takes out line in a hurry. Tested extensively by Orvis' saltwater guides, who found the flyline backing helped them know where a fish was and when it was changing direction. The round Dacron backing won't rot or mildew and stores well on the fly reel. Flyline backing available in 20, or 30 lb. test.