A cryogenic storage dewar is a type of vacuum flask used to store cryogens such as liquid nitrogen or liquid helium. It is also known as a cryogenic vessel. Cryogenic storage dewars are designed for the reliable and long-term storage of samples at very low temperatures. They are typically constructed of stainless steel, aluminum, or a combination of both materials and feature multilayer super insulation to minimize heat transfer into the stored material. They may also include additional features such as pressure relief valves, level gauges, and fill ports.