Sealing liquids and gases in pressure and static applications. Used on hydraulic machinery and pistons. Buna-N : Compounds which are ideally suited for oil resistant applications of all types. Ethylene-Propylene : Compounds that are used extensively for outdoor, weather resistant uses, such as water appliances. Silicone : Excellent as static seals in extreme temperature conditions. Neoprene : Superior sealing materials for the refrigeration industry, resistant to ammonia and Freon.