What is Dry Ice?

This amazing solid form of carbon dioxide requires special handling

Pellets of dry ice sublimating
Jasmin Awad / EyeEm / Getty Images

Dry ice is the solid form of solid carbon dioxide, CO2. Some of the following facts about dry ice that will help keep you safe when working with it—and others are just fun to know.

Dry Ice Facts

  • Dry ice, sometimes called "cardice," is solid carbon dioxide.
  • Dry ice is extremely cold (-109.3°F or -78.5°C). At this temperature, dry ice sublimates from a solid state into a gaseous state or undergoes deposition from gas to solid. Dry ice must be placed in a high-pressure environment in order to form liquid carbon dioxide.
  • The first published observation of dry ice was in 1835 by French chemist Charles Thilorier, who noted the formation of dry ice when a container of liquid carbon dioxide was opened.
  • Dry ice resembles snow or water ice. It's usually sold as chunks or pellets, which appear white because water vapor from the air readily freezes onto the surface. While it looks somewhat like ordinary water ice, it's referred to as "dry" because there's no intermediate liquid phase.
  • Dry ice density usually ranges between 1.2 and 1.6 kg/dm3.
  • The molecular weight of dry ice is 44.01 g/mole.
  • Dry ice is nonpolar, with a dipole moment of zero. It has low thermal and electrical conductivity.
  • The specific gravity of dry ice is 1.56 (water = 1). Dry ice sinks in water and to the bottom of drinks.
  • While the white vapor released when dry ice sublimates does contain some carbon dioxide, it's mostly water fog produced when the cool gas condenses water from the air.
  • When dry ice is added to food—as when making ice cream or freezing fruit—the carbon dioxide carbonates the liquid and can react with water to form dilute carbonic acid which adds an acidic or sour flavor.
  • When dry ice sublimates, some of the carbon dioxide gas immediately mixes with air, but some of the cold dense gas sinks. Carbon dioxide concentrations increase near the floor of a room in which a lot of dry ice is being used.

Dry Ice Safety

  • Contact with dry ice can result in frostbite and cold burns. Avoid allowing any direct contact between dry ice and the skin, eyes, or mouth.
  • Always use properly insulated gloves when handling dry ice.
  • Always use dry ice in a well-ventilated area. Although dry ice and carbon dioxide are nontoxic, since it can sink and displace air near the ground the use of dry ice may present a respiratory hazard. Also, when it mixes with the air, there's more carbon dioxide (less oxygen) in each breath.
  • Do not eat or swallow dry ice.
  • Never seal dry ice in glass jars or other closed containers. The pressure buildup may result in breakage or bursting.