Metal siding comes in a variety of metals, styles, and colors. Corrugated aluminum cladding is also common where a more durable finish is required. Aluminum siding is ideal for homes in coastal areas (with lots of moisture and salt), since aluminum reacts with air to form aluminum oxide, an extremely hard coating that seals the aluminum surface from further degradation. In contrast, steel forms rust, which looks ugly and can weaken the structure of the material, and corrosion-resistant coatings for steel, such as zinc, sometimes fail around the edges as years pass. However, an advantage of steel siding can be its dent-resistance, which is excellent for regions with severe storms—especially if the area is prone to hail.