When you live near the ocean, salt air and humidity can destroy ordinary outdoor furniture in a season or two. If you want a bench that just sits there and looks good without constant sanding, painting, or oiling, the clear answer is high-density polyethylene (HDPE) lumber — often called recycled plastic lumber or marine-grade polymer.
HDPE is made from recycled milk jugs and plastic containers, and it's completely impervious to moisture. It won't rot, warp, crack, or splinter, and it never needs sealing or painting. Salt spray doesn't corrode it, and UV inhibitors keep the color from fading for years. You can hose it down with soapy water and it looks like new. That's as low-maintenance as it gets.
A close second is powder-coated aluminum. It's lightweight, naturally rust-resistant, and the powder coating adds an extra barrier against coastal salt. It won't peel like paint, but if the coating gets scratched, you may see some white oxidation at the scratch — still not structural, but you might need a touch-up pen every few years.
Marine-grade stainless steel (316) is also excellent for hardware and frames, but a full bench made of it can get hot in the sun and shows water spots if not wiped. Teak is beautiful but unless you let it weather to silver-gray (which is a kind of maintenance decision), it needs annual cleaning and occasional oiling to stay golden.
So for truly zero-effort coastal seating, choose HDPE or recycled plastic lumber. Pair it with 316 stainless steel fasteners, and you'll have a bench that survives salt, sun, and sea breeze with nothing more than an occasional rinse.