Aluminum is an extremely lightweight metal, and as a result, anything made out of aluminum is less dense, and therefore lighter, than a similar object made out of a heavier or more dense metal such as steel . Aluminum isn't toxic or magnetic, and is only about one-third as heavy as copper. It also has excellent corrosion resistance. Due to all these factors, furniture made out of aluminum has several important qualities. It also keeps it's shape relatively well, and even though it is light, aluminum furniture is exponentially stronger than plastic. The natural layer of oxide that aluminum forms also makes a good barrier against corrosion. Aluminum is an ideal material for patio furniture, such as tables, chairs, and benches, due to the fact that it requires almost no maintenance. There are three styles of aluminum that are commonly used in the manufacturing of patio furniture. The three types are wrought aluminum, tubular aluminum, or cast aluminum. Wrought aluminum is somewhat like wrought iron except that it is much lighter and doesn't rust, but it is designed to look the same as wrought iron without the weight or propensity to oxidize. Tubular aluminum furniture is the most common type. Tubular aluminum is very light and easy to move, but isn't nearly as durable as the other two types. But by far, the strongest of these three types is cast aluminum. In cast aluminum furniture, molds are created in the desired shape and then molten aluminum is poured into them. When the piece of furniture is removed from the mold, it is polished, and then attached to the other components either by bolting them together, or by welding. The piece of furniture is then coated with a protective covering, possibly paint. This type of aluminum furniture may be the strongest of the three, but since cast aluminum furniture isn't hollow it is much heavier than wrought aluminum or tubular aluminum furniture.