What Is Dry Ice?
QUICK ANSWER
Dry ice is solid carbon dioxide (CO2), which at standard atmospheric pressure sublimates directly from solid to gas without passing through a liquid phase. It's much colder than water ice at –78.5°C and is widely used for shipping perishables, food preservation, theatrical fog effects, and laboratory cooling.
Dry ice is one of the strangest substances in everyday use. It looks like white, foggy chunks of regular ice, but it's much colder and behaves completely differently. Drop it in water and it boils violently, releasing white clouds. Touch it briefly and you can damage skin from the extreme cold. Yet it's commonly used to keep food cold during shipping, to make stage fog, and in dozens of industrial applications. The unusual behavior is because dry ice is solid carbon dioxide.
What is dry ice made of?
Dry ice is solid carbon dioxide (CO2). It's made by compressing CO2 gas and then releasing the pressure, which cools the gas dramatically as it expands. The CO2 partially freezes into a snow-like solid that is then compacted into blocks or pellets. Manufacturing relies on capturing CO2 from industrial processes (like ammonia production, ethanol fermentation, or natural sources) and purifying it. The CO2 in dry ice is the same compound that's in carbonated beverages, exhaled breath, and the atmosphere—just in solid form at very low temperature.
Why is it called 'dry' ice?
Dry ice is called 'dry' because, unlike water ice, it doesn't melt into a liquid. Instead, it sublimates: it transitions directly from solid to gas without passing through a liquid phase. This happens because carbon dioxide's triple point (where solid, liquid, and gas can coexist) is at higher pressure than normal atmospheric pressure. At regular pressure, CO2 can exist as either a gas or a solid but not a liquid. So dry ice 'evaporates' into CO2 gas without ever wetting anything. The cold white fog around dry ice is water vapor condensing from the air, not the dry ice itself.
How cold is dry ice?
Dry ice has a surface temperature of –78.5°C (–109.3°F), much colder than water ice's 0°C (32°F). This extreme cold makes dry ice useful as a coolant but also potentially dangerous. Direct skin contact for more than a moment can cause frostbite-like burns. Dry ice should be handled with insulated gloves or tongs and never with bare hands. Containers holding dry ice must allow gas to escape; in sealed containers, the sublimating gas builds pressure that can cause explosions. Cars and small enclosed spaces shouldn't contain large amounts of dry ice because the CO2 can displace oxygen.
What is dry ice used for?
Dry ice is widely used for shipping perishable goods that need to stay frozen during transport, like seafood, frozen foods, and biological samples. Medical facilities use it to preserve specimens and ship pharmaceuticals. The entertainment industry uses dry ice to create thick, low-lying fog for stage shows, movies, and Halloween effects. Laboratories use it for various cooling needs. Food service uses it for ice cream socials, dramatic presentations, and to keep food cold at outdoor events. Some metal-shrinking and cleaning processes also use dry ice.
Dry ice is solid carbon dioxide that sublimates directly from solid to gas without melting, making it useful for shipping, refrigeration, and special effects. Much colder than water ice and harmless when used properly, dry ice has unique properties from CO2's chemistry rather than just being cold water in another state.
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