Valve cover gaskets are manufactured from a silicone rubber compounded especially for lubricating oil resistance and low compression set. It has a recommended temp. operating range of –67 to 446 F and will remain flexible while operating in the noted temp. range. One of the biggest benefits of replacing the factory cork gaskets with the Silicone rubber gaskets is that they are reusable and are easy to work with and are 1/8" thick silicone rubber.