Science, Tech, Math › Science Why Dry Ice Makes Fog or Smoke Special Effects Share Flipboard Email Print Andrew W.B. Leonard, Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated August 19, 2019 Why you put a piece of dry ice in water, you'll see a cloud of what looks like smoke or fog billow away from the surface and down toward the floor. The cloud is not carbon dioxide, but actual water fog. How Dry Ice Produces Water Fog Dry ice is the solid form of carbon dioxide, a molecule that is found as a gas in the air. Carbon dioxide has to be cooled to at least -109.3 °F to become a solid. When a chunk of dry ice is exposed to room temperature air it undergoes sublimation, which means it changes from a solid directly into a gas, without melting into a liquid first. Under ordinary conditions, this occurs at the rate of 5-10 pounds of dry ice converting into gaseous carbon dioxide per day. Initially, the gas is much colder than the surrounding air. The sudden drop in temperature causes water vapor in the air to condense into tiny droplets, forming fog. Only a small amount of fog is visible in the air around a piece of dry ice. However, if you drop dry ice in water, especially hot water, the effect is magnified. The carbon dioxide forms bubbles of cold gas in the water. When the bubbles escape at the surface of the water, the warmer moist air condenses into lots of fog. The fog sinks toward the floor both because it is colder than the air and because carbon dioxide is denser than air. After a time, the gas warms up, so the fog dissipates. When you make dry ice fog, the concentration of carbon dioxide is increased near the floor. Ready to try it yourself? Here's how to make dry ice fog, safely.