Sinn watch u1 s silicone black 1010020 silicone black the case and crown of thesinn watches u1 s are made of high strength seawater resistant german submarine steel as well as having extreme seawater resistance this material possesses the highest level of non magnetic properties thanks to its captive design it is virtually impossible for the divers bezel with minute ratcheting to become detached from the case as a result of hard knocks the watch has been checked for pressure resistance an