Honestly, after years of specifying coatings for public furniture, I’d say the most durable finish for an outdoor bench in a high-traffic transit station is a two-part catalyzed polyurethane, often applied over an epoxy sealer if the bench is wood. For metal benches, a TGIC polyester powder coat is your best bet. Both systems resist the daily abuse of commuters, graffiti, UV exposure, and cleaning chemicals far better than standard paints or varnishes.
Here’s why. Catalyzed polyurethane cures by chemical reaction, not just solvent evaporation, forming a hard, flexible film that won’t chip or peel easily. Over wood, an epoxy sealer first penetrates the grain and stabilizes the surface, blocking moisture and tannins. Then two to three coats of marine-grade aliphatic polyurethane (like a 2K PU from brands such as Interlux or Awlgrip) provide excellent abrasion resistance and color retention. This combination can easily last 7–10 years before needing a recoat, even with hundreds of people sitting on it daily.
For powder-coated metal benches, choose a TGIC polyester or polyurethane powder coat with a minimum film thickness of 3–4 mils. Powder coating is electrostatically applied and baked on, creating a seamless, impact-resistant shell. It shrugs off scratches, salt, and solvents. Just make sure the metal is properly pretreated (zinc phosphate or similar) before coating; otherwise rust will creep under the finish.
A quick note on maintenance: whatever finish you choose, specify satin or matte sheen rather than high gloss. Gloss shows wear, fingerprints, and graffiti much faster, and touch-ups on glossy catalyzed coatings are nearly impossible to blend invisibly. Satin hides scuffs and can be lightly sanded and recoated in small areas without a full strip.
If you’re limited to a one-part system, moisture-cured urethane (MCU) is a decent runner-up for wood, but it’s not as tough as a true 2K polyurethane. For metal, avoid liquid-applied paints—they simply won’t survive constant abrasion from bags, umbrellas, and metal zippers. Stick with powder or catalyzed liquid coatings.
In short, the most durable finish is a system, not a single product: epoxy sealer + catalyzed polyurethane for wood, or TGIC polyester powder coat for metal. Both will give you the longest service life in a brutal, high-traffic transit environment.