That's an excellent and very practical question for anyone living near the ocean. Salt air is incredibly corrosive and can ruin ordinary outdoor materials in just a season or two. Based on durability and real-world performance, here’s the breakdown.
The top contender is Marine-Grade Stainless Steel (Type 316). This is the gold standard. It contains molybdenum, which provides exceptional resistance to pitting and rust from chlorides (like salt). While it's a significant investment, it will look good and function flawlessly for decades with minimal care. A close second is Hot-Dipped Galvanized Steel. The thick zinc coating sacrificially protects the underlying steel from rust. It will develop a patina over time, but it remains structurally sound for many years. Just avoid scratching the coating.
Materials that often struggle in coastal environments include standard Powder-Coated or Painted Steel. Once the finish is compromised by a chip or scratch, salt air accelerates rust underneath. Common Plastics (like polyethylene) can also become brittle and fade rapidly due to UV exposure, which is often intensified near the coast.
My final, natural advice? For a permanent solution, choose marine-grade stainless steel. For a cost-effective and still very durable option, go with hot-dipped galvanized steel. Always ensure any bin has drainage holes to prevent salty water from sitting inside. A quick rinse with fresh water every now and then will also significantly extend the life of any coastal bin.