Traditional Dacron fly line backing featuring high strength and low stretch. A good compromise between Thinness and the ability to make blind splice loops. A high quality super-smooth braid that is reliable.
Well, it does the intended job, but one additional thing that I like about it is that I switch reel spools containing different fly line types during a day's outing, & by using different backing colors for each, I can grab the correct spools at a glance of the color I've designated for each Flyline.