RIOs newest tippet material is an ultra-strong, 100% fluorocarbon with exceptionally high tensile strength. The material is very easy to tie knots in, with high knot strength and a smooth finish that ensures knots seat easily and tightly. The high break strength to diameter ratio makes this a fantastic fluorocarbon for the trout fly fisher. RIO is proud to introduce half sizes of core trout diameters, giving anglers an extra choice when faced with the decision to choose between, say 4X and 5X. Our new 6.5X, 5.5X and 4.5X sizes will make those decisions easier.