Fishing line comes in many forms these days. All have their advantages in certain situations. From the dependable monofilament line, which has been around since the late 1930s, to relative newcomers, like fluorocarbon line and braided "super lines," fishermen have many good options to choose from.
Monofilament line is produced by melting various polymers together and then extruding the material through a die to form a single strand of line. The line's diameter and break strength are controlled by the size of the hole in the die. Monofilament can be have different characteristics, based on the polymers used. Some monofilaments, like Berkley Trilene XL, are formulated to be less stiff or "soft" so they won't coil or twist during use. Other lines, like Berkley Trilene XT, are formulated to be more abrasion-resistant and have a high break strength for fishing around heavy cover, like weeds and stumps.
Braided lines, such as the Spectra and Dyneema brands, have made a resurgence in popularity, thanks to low-stretch, high-strength materials. Small strands of these materials are wound together to form a single line. These fishing lines have been dubbed "superlines" because of their high break strength and small diameters. For example, Berkley's Fireline boasts a break strength of 20 lb. test in a regular 8 lb.-test monofilament diameter. These thin, strong lines work well when fishing in deep water because they do not absorb water and have very little stretch, allowing anglers to feel light-biting fish.
Fluorocarbon line has gained immense popularity over the last decade, thanks to a chemical composition that makes it nearly impossible for fish to see. Fluorocarbon line is manufactured the same way as monofilament, but there is a difference in the polymers used to make each line. Monofilaments use a nylon-based polymer; fluorocarbons use a fluoropolymer. The properties of a fluoropolymer give it a lower optical density, which refracts light instead of reflecting it, making it less visible than nylon. Another advantage to fluorocarbon line is a harder surface, which resists abrasion and is more dense, helping it to sink faster.