Fluorocarbon fishing line is made from polyvinylidene fluoride. The line does not absorb water, which is one of its biggest selling points. It stays strong when wet.
The near invisibility of fluorocarbon line when in the water is due to having nearly the same refractive properties of water. Fish cannot detect the line, making it an attractive line to use where fish are under heavy pressure from anglers.
Anglers will often opt to use a fluorocarbon leader attached to their monofilament line. These hard-to-see leaders help them catch more fish.
Because fluorocarbon does not stretch as much as monofilament line and is smaller in diameter, it is sensitive to a biting fish and makes setting the hook easier.
Fluorocarbon fishing line is stiffer than other lines. It is also much more expensive.