Compression (mismatched) seals are created when the CTE, coefficient of thermal expansion and contraction, of the header body or housing greatly exceeds that of the glass or electrodes. During the firing process, the metal materials, usually stainless steel, expand at a great rate than glass. During cooling, the metal contracts into the already solidifying glass to form an extremeley robust compression bond. This type of seal is frequently specified for extreme high pressure applications. The working pressure can be as high as 14,000 PSI range. Materials used by Complete Hermetics can include: Body Materials: Cold rolled steels, Stainless steel, Inconel, etc. Glass Materials: Corning 9010/9013 (Alkali Barium), Soda lime, Lead silicate, etc. Electrodes Material: Alloy 52, Copper Cored 52 Alloy, Alloy 42, etc. Typically Compression Seals withstand temperatures ranging from -250°C to 400°C. Allowable operating temperatures would be from -60°C to 200°C under thermal cycling and shock.