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 & when it was changing direction. The round Dacron backing won't rot or mildew & stores well on the fly reel. Flyline backing available in 20, or 30 lb. test.