Supercritical fluids have the low viscosity of gas and the high density of a liquid, making it impossible to liquefy the matter using any amount of pressure. However, it is possible to go from a gas to a liquid without crossing the boundary between the vapor and liquid phase using a supercritical fluid just by lowering the temperature of the liquid. The densities and viscosity of a supercritical fluid are subject to change when pressure or temperature is tampered with, and the supercritical fluid of a substance can have very different properties than the regular fluids.