A Knotless, Tapered 100% Fluorocarbon Leader For The Utmost In Stealth. RIO's Fluoroflex trout leaders are made of 100% fluorocarbon, and are the perfect solution for when a nearly invisible presentation is required in clear water and for spooky fish. Each leader has high abrasion resistance and excellent tensile and knot strength, and have a long butt section that will turn over flies effortlessly.