Nylon (technically called polyamide) itself is a very stretchy fiber and so is the webbing woven from it. This material revolutionized the world of rock climbing because it allowed ropes to absorb more energy during a lead fall, thus reducing the load transferred to the placed protective gear and the climber creating a safer environment. Slackliners adopted nylon webbing because it was readily available and cheap. Tubular nylon is the most common webbing used in primitive systems, but nylon also comes as flat, slackline specific webbing. It generally is soft on the skin and is the most friendly webbing to catch when at low to mid tensions.
Nylon is, however, much harder to bring to a walkable tension over long distances. This is due to the significant stretch, making it difficult if not impossible to tighten with a ratchet. One inch tubular nylon can be threaded with 11/16” webbing for extra strength and reach theoretical strengths of up to 8’500 lbf (38 kN) in breaking strength. Nylon is mostly used for lines up to 150ft (~50m), after that the length of the tensioning systems tends to take on absurd dimensions.