Titan Highline® is completely nickel-free and is suitable for sensitive and very allergic people. It is half as heavy as steel, and is one of the five substances that are best accepted by the body. It is not actually the titanium itself that is so good for the body, but the layer of titanium oxide that forms on the surface. The oxide layer also acts as a barrier against other substances in the titanium leaking into the body. If the titanium oxide surface is worn away, a new layer is formed immediately.