A mist or fog is a microscopic suspension of liquid droplets in a gas such as the Earth's atmosphere. The term is most often used with respect to water vapor. The size of the liquid particles is usually in the range of 1 to 1,000 nanometers. Do not confuse a fog with a vapor. Vapors are composed of single, gas-phase molecules whereas mist droplets are liquid-phase and contain thousands or millions of molecules. Many, but not all, vapors are colorless and therefore invisible, whereas fogs can generally be seen and reduce visibility. Vapors do not wet objects that they contact (although they may condense on or react with a surface) whereas mists generally do. See the vapor entry for more information about solids, liquids and gases. Do not confuse mists with fumes which are solid airborne particles.