SUNPASS FEP-Encapsulated 'O' Rings: A Robust Core of Silicone (VMQ) Elastomer Enveloped by a Seamless FEP Fluoropolymer Sheath. These Rings are Fully Interchangeable with Standard Elastomeric 'O' Rings and Solid PTFE 'O' Rings, Offering Unparalleled Performance and Reliability.