O-rings are among the most widely used sealing components in industrial equipment, automotive systems, aerospace applications, and fluid power systems. Despite their simple appearance, O-rings must perform reliably under extreme pressures, temperatures, and chemical exposures. The key to achieving long service life and leak-free performance lies in selecting the right material for each specific application. With numerous elastomer options available—including NBR, FKM, EPDM, Silicone, and others—engineers and maintenance professionals must understand the differences in chemical compatibility, temperature range, and mechanical properties. This article provides a comparative overview of the most common O-ring materials and offers practical guidance for material selection.