When angling became popular in Europe, a book published way back in 1496, describes how fisherman braided high quality horsehair for fishing line that was void of weak spots and imperfections, and was painstakingly hand braided with a special tool.
By about 1908, silk line replaced horsehair. The woven silk line threads were longer and much stronger than horsehair. Silk line could also be woven by machines, unlike the laborious handwoven horsehair line. Silk line had to be rinsed and dried on open spools after every use and ultraviolet light from the sun would cause damage to the silk. Silk lines were easily cast, but also easily tangled. As well, silk line would float if covered with oxidized linseed oil or sink if untreated.
Then, in 1924, Captain Lester Crandall and the Ashaway Line and Twine Manufacturing Company in Rhode Island, developed Cuttyhunk (linen) fishing line, which quickly became the standard for fisherman everywhere.
Saltwater fisherman immediately started using linen line for catching big-game fish, while their freshwater counterparts were still using silk line. But both linen and silk line demanded special care to avoid deterioration caused by UV light, bacteria and mold, a nagging issue that needed to be addressed.
Fortunately, in 1938, DuPont announced the invention of Polyamide fibers, and by working with DuPont, Ashaway produced the first ever nylon fishing line by 1939. Later in 1952, Ashaway introduced the first ever Dacron line, and by 1954, nylon fibers were introduced as the first Monofilament line. A by-product of crude oil processing, nylon monofilament is formed through an extrusion process in which molten plastic is formed into a single strand through a special die.
The next breakthrough was Fluorocarbon line, invented and first introduced to the fishing market by Seaguar in 1971, as a high-performance, ultra-clear line to help anglers catch more fish.
A little later down the road, Spectra was developed at Honeywell in 1991, which had a tiny diameter and extreme strength, allowing for new ultra-light weight, powerful, small reels to quickly replace their bulky, heavier predecessors, because there was no longer a need for wider spool line capacities. So ultimately, Spectra became the line that changed sportfishing forever.