From an outdoor bench factory perspective, the most honest answer is that durability depends on how the bench is built, but the materials behave very differently. If you are comparing a bare aluminum bench with a recycled plastic bench for a busy school playground, powder-coated aluminum is generally stronger for the load-bearing structure. It resists rust, does not rot, holds up well to heavy daily use, and can be designed with reinforced legs and vandal-resistant fixings. However, aluminum can become hot in direct sun, may dent under severe impact, and needs a good powder coating to prevent scratches and corrosion. Recycled plastic, usually HDPE, is excellent for comfort and safety because it is splinter-free, rot-resistant, insect-resistant, and does not rust. It also handles wet weather well and needs little maintenance. Its weak point is structural rigidity: thick recycled plastic slats can sag under heavy load or heat unless they are supported by a strong steel or aluminum frame, and lower-grade plastic may fade or chalk over time. For a school playground, the most durable and practical choice is often a hybrid bench: a powder-coated aluminum frame with UV-stabilized recycled plastic slats, rounded edges, and secure fixings. If you must choose one material for the main structural body, aluminum is more durable under heavy school use. If you are choosing the seating surface for comfort, safety, and splinter-free contact, recycled plastic is the better fit. So for maximum durability from an outdoor bench factory, specify aluminum for the frame and recycled plastic for the seat and back slats, then confirm the wall thickness, UV rating, coating quality, and load test standard before ordering.