Also monofilament in structure, these lines are made with PVDF, commonly known as fluorocarbon. 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.