The Rolex Explorer II 42mm is sporting a Rubber B strap in Mandarin Orange. The bracelet is made of Vulcanized Rubber, the most respected and revered material in the rubber watch strap industry, which is why it is used by brands such as Audemars Piguet, Omega, Hublot, and Louis Vuitton to name a few. In this photo, you will notice the Rubber Bs micro-calibration and integration with the Rolex Explorer II 42mm watch case.