The popularity of fluorocarbon is largely due to these lines being invisible to fish. Unlike nylon, fluorocarbon refracts light nearly identically to water. In addition, fluorocarbon lines are fast sinking due to higher density. Since fluorocarbons do not absorb water, they also maintain their original strength and abrasion resistance. These lines are higher priced than nylon monofilaments, and require greater care in knot tying. The most flexible, easiest casting fluorocarbon. 100% fluorocarbon has a similar refractive index to water, so fish can't see it. Best Vanish formula ever, with 20% better shock strength, improved knot strength and easier to handle. Non-absorbing fluorocarbon maintains strength and abrasion resistance underwater. It is extremely abrasive resistant and has excellent knot strength. Like all Vanish products is virtually invisible to fish. A handy feature indeed!