The rotating bezel of modern Rolex Submariner models is made from Cerachrom, Rolex’s proprietary ceramic material. Cerachrom inserts are designed to resist scratches, corrosion and fading from ultraviolet light, making them suited to a bezel exposed to seawater, sunlight and frequent handling.
Rolex began introducing Cerachrom bezels to the Submariner range in the 2000s. The material is an exceptionally hard ceramic, and Rolex colors it throughout the material rather than applying a thin surface coating. The engraved bezel numerals are filled with a precious-metal coating, helping them remain legible against the insert.
Earlier Submariners used aluminum bezel inserts, so aluminum is a historically correct answer for many vintage and older examples but not for the modern models specified here. Steel is used elsewhere in many Submariner cases and bracelets, while sapphire is the crystal material covering the dial. Cerachrom also gives the bezel its familiar glossy, high-tech appearance and supports the model’s unidirectional timing function for divers.