A supercritical fluid (SCF) is neither a liquid nor a gas nor a solid. SCFs are non-condensable fluids at a temperature and pressure above the substance’s inherent “critical point”.

Such fluids have both liquid and gas properties; the density of an SCF is several hundred times that of the gas form, making it as similar to a liquid as possible, but the viscosity is comparable to that of a gas. In other words, an SCF is a fluid with a high molecular density comparable to that of a liquid while combining the same kinetic energy as gas molecules.

One of the most pronounced features of an SCF is the combination of a high solvency and high diffusivity with no surface tension.