A dewar cylinder is a type of container used to store liquefied gases at extremely low temperatures. It is named after its inventor, Sir James Dewar, who was a Scottish chemist and physicist. Invented in the late 19th century, dewar cylinders are used extensively in scientific research, medical applications, and industrial processes.

In scientific research, dewar cylinders are commonly used to store superconducting materials such as liquid helium or liquid nitrogen, which are used in experiments involving low-temperature superconductivity. They are also used to store cryogenic liquids such as liquid oxygen and liquid nitrogen, which are used in the study of molecular biology and chemistry.

When stored at extremely low temperatures, liquefied gases can rapidly expand when exposed to ambient temperatures, which can result in an explosion or pressure release. Additionally, the potential for frostbite and other cold-related injuries must be taken into account when handling dewar cylinders.