Selecting Compounds Selecting the right compound for the application of the part you need is very important. The wrong compound could result in the failure of the part in a very critical application. When selecting a compound, you will want to consider the following: Compatibility with the media to be sealed (oils, water, acids, minerals, etc.) Temperature range to which the seal will be exposed General properties required to resist material degradation (Ozone) Durometer (hardness) best fitting the application Compatibility between fluid media and elastomeric compounds is critical in every application. The selection of base elastomers is already large enough to cover all but the most exotic fluids or extreme temperatures and pressures. Volume swell and physical property changes after exposure are the usual criteria, with static seals permitting greater latitude in property changes. Chemically similar structures tend to dissolve mutually, and are to be avoided in the selection of seal materials. In many cases the seals must be compatible with several fluids, and no single composition is ideal. This necessitates selecting a material that adequately meets the critical criteria of any application.