Synthetic

Strong and weatherproof

Nylon stretches (and absorbs shock); polyester barely stretches (and holds knots steady); both shrug off rot, mildew, and sun better than any plant fiber.

Nylon vs polyester

nylon      stretches ~25% — good for shock, anchor
polyester  stretches ~10% — good for static lines
both       rot-resistant, UV-resistant
knots      need extra friction (slippery)

Best for

Camping, boats, load lines, and anything left outside year-round. Slicker than natural fiber — back up your hitches.