The XO 100 is our most advanced fly line yet. XO has a thin and durable DuraSlim™ coating. DuraSlim™ enables us to manufacture a line with thinner running line than before without sacrificing durability. It also features varying hardness coatings in different parts of the line; the head being softer allowing you to push arrow shaped tight loops and the running line being harder for carrying extra-long overhangs and ultimate shoot-ability. The fly line has super small loops on both ends and clear markings of the line weight near the tip of the line. Phthalate free.