These O-Rings Are Made Of FEP Teflon On the Outside For Chemical Inertness and Silicone On the Inside For Outstanding Resilience. They Withstand Dry Heat Conditions As Ordinary Silicone and Are Virtually Impervious To Most Solvents and Chemicals Due To Their Teflon Cover. The Resin In FEP Teflon Meets Or Exceeds L-P389A and ASTM D2116 Requirements and I.D. FDA Approved. Temperature Range Is -75°F To 400°F. Hardness Is 65-75 Shore A Durometer. Clear In Color With an Amber Center.