At Sinn, only high-quality and robust materials are used when making watches. The case and crown are made of German submarine steel to achieve the high strength of the U212. While the steel case is unbreakable and crack-resistant, submarine steel protects the watch against saltwater. This makes the Sinn U212 an ideal and reliable wristwatch, especially for divers. The size-adjustable leather or silicone strap does the rest.