A critical point dryer is a device that uses the principle of supercritical drying to remove liquid from delicate samples without causing damage or deformation. It is commonly used for preparing biological specimens for scanning electron microscopy (SEM) or for drying microelectromechanical systems (MEMS) and gels. The process involves replacing water with an intermediate fluid, such as ethanol or acetone, and then with liquid carbon dioxide (CO2), which has a low critical point of 31 °C and 74 bar. The liquid CO2 is then heated and depressurised to reach the critical point, where it becomes a gas without crossing the liquid-gas interface. This avoids the surface tension effects that would otherwise distort or collapse the sample structures.