A vacuum insulated evaporator (VIE) is a form of pressure vessel that allows the bulk storage of cryogenic liquids including oxygen, nitrogen and argon for industrial processes and medical applications.^[1]

The purpose of the vacuum insulation is to prevent heat transfer between the inner shell, which holds the liquid, and surrounding atmosphere.^[2] Without functioning insulation, the stored liquid will rapidly warm and undergo a phase transition to gas, increasing significantly in volume and potentially causing a catastrophic failure to the vessel due to an increase in pressure. To combat such an event, VIEs are installed with a pressure safety valve.

To remain a liquid, the vessel contents must be kept at or below its critical temperature. The critical temperature of oxygen is −118 °C; above this temperature, applying more pressure will not result in a liquid, but rather a supercritical fluid.^[3]