Nylon rope has a lot of stretch (up to 40%) and is very strong for its size, allowing it to absorb shock loads well. However, when it is wet it can lose up to 25% of its strength. It wears well, resists mildew and rot, and does not float. Nylon three-strand is the preferred line for dock lines since it stretches sufficiently to dampen the shock of wave action and wind against your cleats. Just make sure it does not stretch too much for the situation in which you use it.