Hermetic seals provide a vacuum or leak-tight seal, insulate or channel electricity, and prevent the ingress of contaminants. They are made of ceramic, glass, or metal materials and joined in a specific configuration by furnace brazing. Containers that use hermetic sealing are able to withstand high temperatures and hold pressures up to 150,000 pounds per square inch (psi). Common types of hermetic seals include metal-to-metal seals, ceramic-to-metal seals, and glass-to-metal-seals. Metal-to-metal hermetic seals are created by firing two or more metal components with the addition of gold, silver, nickel or copper filler materials. Ceramic-to-metal hermetic seals are run through a high-temperature furnace to create a final assembly with a permanent hermetic bond. The hermetic seal is then coated with a metallic pattern. There are two types of glass-to-metal hermetic seals: matched seals and mismatched (compression) seals. Matched glass-to-metal hermetic seals are made of metal alloys and components that share similar thermal expansion characteristics. Mismatched or compression glass to metal hermetic seals feature a steel or stainless steel metal housing that has a higher thermal expansion rate than the glass component. Upon cooling, the metal housing contracts around the glass, creating a hermetic seal that is reinforced both chemically and mechanically.