Very strong and wear-resistant Weatherproof and durable material Warm and natural appearance The standard material thickness of our CorTen Steel planters is 2mm, although they can also be produced in 3-4 and 5mm. CorTen Steel, also known as weather resistant steel, is a steel alloy made of iron which has copper, silicon, nickel and chromium added. As soon as CorTen Steel is exposed to the elements it will naturally weather and develop a protective layer of rust, this can take several months. This natural fixed coating of rust provides protection against further corrosion. Characteristic of CorTen Steel is the brown rust orange colour and its longevity. Made in Europe.