Dry ice does not melt under normal conditions. Instead, it sublimates, meaning it transitions directly from a solid into carbon dioxide gas without ever passing through a liquid phase. At standard atmospheric pressure, this happens at around −78.5 °C (−109.3 °F).1Journal of Cleaner Production. Industrial use of dry ice blasting in surface cleaning The process looks a lot like evaporation, and people sometimes describe it as “melting” because the solid block visibly shrinks, but what you are watching is a substance skipping the liquid stage entirely and becoming a gas.
Why Dry Ice Skips the Liquid Stage
Whether a substance exists as a solid, liquid, or gas depends on both temperature and pressure. For most materials you encounter daily, like water ice, warming them up at normal atmospheric pressure takes them from solid to liquid to gas in the familiar order. Carbon dioxide behaves differently because its triple point, the specific temperature and pressure where solid, liquid, and gas can coexist, sits well above normal atmospheric pressure. Precise measurements put that triple point temperature at about −56.6 °C.2Metrologia. Realization of the triple point of carbon dioxide in a transportable cell using long-stem SPRTs But the pressure required to reach that triple point is roughly 5.1 atmospheres, or about five times the pressure at sea level.
Because you live and work at roughly 1 atmosphere, that liquid phase is simply not accessible. When you warm dry ice at normal pressure, the molecules gain enough energy to fly apart into gas long before the conditions for a liquid state are met. The solid just converts directly to a gas. This is sublimation, and it is the same process that causes frost to vanish from a car windshield on a cold, dry morning without first becoming a puddle. Carbon dioxide is just a much more dramatic example because the sublimation temperature is so far below normal air temperature. Even a freezer at −18 °C is roughly 60 degrees warmer than dry ice, so sublimation begins immediately upon exposure to just about any environment you would encounter.
How Quickly Dry Ice Disappears
The rate at which dry ice sublimates depends heavily on its shape and size, specifically the ratio of surface area to volume. A study measuring mass loss across different dry ice formats found that pellets and small chunked blocks lost roughly 2.5 to 2.8 percent of their weight per hour, while larger blocks with less surface area relative to their volume lost only about 1 to 1.6 percent per hour.3Engineering Reports. Dry ice sublimation performance as affected by binding agent, density, and age In practical terms, a bag of small dry ice pellets left at room temperature will shrink noticeably within an hour or two, while a large 10-kilogram slab stored in a well-insulated cooler can last a couple of days.
This is why suppliers sell dry ice in different forms for different jobs. Pellets are designed for applications like blast cleaning, where rapid sublimation is actually the point. Large blocks are sold when you need sustained cooling over time, such as keeping food frozen during a power outage or shipping temperature-sensitive materials. The insulation around the container matters just as much as the form factor. A standard styrofoam cooler slows heat transfer enough to extend the life of a block meaningfully, while leaving dry ice in an open tray at room temperature guarantees fast disappearance.
What the Fog Actually Is
The dramatic white cloud that billows off dry ice, especially when placed in water, is one of the most recognizable and most misunderstood things about it. Many people, including some science teachers, explain the fog as atmospheric water vapor condensing onto the cold carbon dioxide gas as it sublimes. That explanation turns out to be wrong.4Journal of Chemical Education. A Molecular Explanation of How the Fog Is Produced when Dry Ice Is Placed in Water
When you drop dry ice into warm water, the sublimation rate goes through the roof. Carbon dioxide gas forms rapidly at the surface of the solid, and because it is produced underwater, it rushes upward as bubbles. Those bubbles burst at the water’s surface and launch tiny water droplets into the air. Meanwhile, the gas escaping from the water is extremely cold, and it chills the surrounding air enough to push the water vapor already present in that air past its dew point. The result is a dense, ground-hugging fog made primarily of tiny liquid water droplets, not carbon dioxide gas itself. CO₂ is invisible and odorless. What you see is water.
When dry ice just sits in open air without water, you still get some wispy white fog for the same basic reason: the sublimating gas is cold enough to condense moisture out of the surrounding air. The effect is just less dramatic because you lose the bubble-bursting mechanism that launches water droplets everywhere. In very dry environments, the fog is barely visible at all.
The Hovering Trick
If you place a flat piece of dry ice on a smooth, warm surface like a polished countertop or a metal table, it scoots around with eerily little friction, as though it were floating. It essentially is. The gas produced by sublimation forms a thin cushion between the solid dry ice and the surface beneath it, a phenomenon related to the Leidenfrost effect. Researchers have studied this using dry ice disks on various substrates and confirmed that the sublimation-driven gas layer acts as a lubricant, dramatically reducing friction.5PubMed. Dry ice hoverboard: Friction reduction by the Leidenfrost effect The gas is continuously replenished as long as the temperature difference between the dry ice and the surface drives sublimation.
This principle has been taken further. Researchers have built small dry ice “hovercrafts” that float on water and can be steered through channels by designing structures that direct the escaping gas.6PubMed Central. Self-Propelled Hovercraft Based on Cold Leidenfrost Phenomenon These experiments are more about exploring low-friction physics than building anything practical, but they illustrate just how vigorous the gas production from sublimation can be. The dry ice is its own propulsion system.
Can Dry Ice Actually Melt?
Yes, but you will never see it happen in your kitchen. Liquid carbon dioxide exists only when the pressure is above that triple point threshold of about 5.1 atmospheres. If you placed dry ice inside a sealed, pressure-rated vessel and allowed the sublimating gas to build up enough pressure, or if you used an external pressure source, you could eventually push past the triple point and watch the solid carbon dioxide become a liquid. This is exactly what happens inside high-pressure CO₂ fire extinguishers and in some industrial processes. The liquid is kept in that state only by the pressure of the sealed container; the moment you release the pressure, the liquid flashes back into a mix of gas and solid snow.
So the answer to whether dry ice “melts or evaporates” is technically “it can do either, but under everyday conditions it only sublimates.” The liquid phase of CO₂ is a high-pressure curiosity that most people will never encounter outside of an industrial setting or the inside of a fire extinguisher.
Handling Dry Ice Safely
Because sublimation is constant and produces large volumes of gas, dry ice creates two categories of hazard that catch people off guard: cold burns and carbon dioxide buildup.
The cold burns are intuitive. At −78.5 °C, direct skin contact causes frostbite-like injuries within seconds. Insulated gloves, tongs, and common sense go a long way. The less intuitive danger is the gas itself. Carbon dioxide is heavier than air and accumulates in low-lying, poorly ventilated spaces. In small concentrations, it is harmless, since your body produces it with every breath. But when excess CO₂ builds up in the air around you, it lowers your blood’s ability to carry oxygen and triggers a cascade of effects on your respiratory and nervous systems.7PubMed Central. Lessons Learned: Asphyxiation Hazard Associated with Dry Ice Symptoms at moderate concentrations include headaches and dizziness. At high concentrations, in a small room or enclosed vehicle with a large quantity of sublimating dry ice, unconsciousness and death are real risks.
The other danger stems from containment. Sealing dry ice in an airtight container is a recipe for a pressure explosion, because the solid-to-gas transition expands the volume enormously. A single kilogram of dry ice produces roughly 500 liters of gas at room temperature. Placing dry ice in a tightly sealed plastic bottle, a glass jar, or even a poorly vented cooler can create enough pressure to rupture the container violently. Any container used for dry ice needs to allow gas to escape freely.
Cold Chain Logistics and Vaccine Shipping
The sublimation behavior of dry ice is central to cold chain logistics, the network of temperature-controlled storage and transport that keeps everything from frozen food to biological samples viable. Dry ice’s chief advantage over regular water ice is temperature: it keeps items far colder, down to about −78 °C, and it leaves no liquid melt water behind. Its disadvantage is that it is always disappearing. You cannot stop sublimation; you can only slow it with insulation.
This tradeoff was thrown into sharp relief during the distribution of mRNA COVID-19 vaccines, which required ultra-cold storage. One approach involved topping off shipping containers with fresh dry ice every five days to maintain stable temperatures. In practice, that proved difficult in remote and rural areas where dry ice supply chains were thin, and the cost and complexity of shipping a substance that is continuously converting to gas added logistical headaches.8PubMed Central. Management of COVID-19 vaccines cold chain logistics: a scoping review Dry ice is also classified as a hazardous material for air transport because of the gas it produces, which limits how much can be carried on a single flight.
In less extreme cold chain applications, the steady sublimation is actually useful. Shipping frozen food in a styrofoam box with dry ice works precisely because the gas escaping through the box’s imperfect seal means the container does not pressurize, the food stays deeply frozen for a day or two, and there is no puddle of melt water soaking the packaging when it arrives.
Mosquito Traps and Other Sublimation-Dependent Uses
The steady, predictable release of carbon dioxide gas from sublimating dry ice has been put to work in entomology for decades. Female mosquitoes locate hosts primarily by following plumes of exhaled CO₂, so traps baited with dry ice are the standard tool in mosquito surveillance programs.9PubMed. DO IT YOURSELF: INSULATED DRY ICE CANISTERS FOR CO2 BAITED MOSQUITO TRAPS The sublimating dry ice mimics a breathing animal, luring mosquitoes to the trap. Field comparisons have shown that traps baited with dry ice pellets capture significantly more mosquitoes than traps using pressurized CO₂ tanks or yeast-based CO₂ generators.10PubMed. Field Comparison of Carbon Dioxide Source with Biogents Sentinel-2 and Pro Traps for Adult Aedes Mosquito Surveillance The pellets produce a more natural, fluctuating gas plume that apparently mimics real breathing patterns more convincingly than a steady flow from a pressurized cylinder.
Dry ice blasting is another application where sublimation is the entire point. In this industrial cleaning method, dry ice pellets are accelerated by compressed air and fired at a surface. On impact, the pellets sublimate almost instantly, and the rapid expansion from solid to gas helps lift contaminants off the surface. Because the dry ice disappears into gas, there is no secondary waste to clean up, unlike sand or bead blasting. The cleaned surface is left dry and free of residue. This technique is used in food processing plants, aerospace manufacturing, and historical restoration where gentle but thorough cleaning is needed.
Dry Ice on Mars
Earth is not the only place where carbon dioxide sublimation shapes the landscape. Mars has a thin atmosphere composed of about 95 percent CO₂, and during the Martian winter, temperatures at the poles drop low enough for atmospheric carbon dioxide to freeze directly onto the surface, forming seasonal polar caps of CO₂ ice, essentially planetary-scale sheets of dry ice. When spring arrives, these caps sublimate, and the process is far from gentle.
Observations of the northern polar cap show that spring sublimation is one of the most dynamic geological processes currently active on Mars, powerful enough to reshape dune formations and alter surface features from one year to the next.11Icarus. Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes At the south pole, the process is even more dramatic. Researchers have proposed that the seasonal ice cap forms as a translucent slab of CO₂ ice. Sunlight penetrates through the slab and warms the ground beneath it, causing the base of the ice to sublimate. The trapped gas builds up under pressure until it escapes in violent jets that carve spider-like channels into the terrain and shoot dark plumes of dust and sand into the air.12PubMed. CO2 jets formed by sublimation beneath translucent slab ice in Mars’ seasonal south polar ice cap
These Martian geysers are driven by exactly the same physical process as the white fog rolling off a block of dry ice on your counter, just scaled up to a planet where the atmosphere itself freezes and sublimates with the seasons. It is a vivid reminder that sublimation is not some niche laboratory curiosity. On Mars, it is one of the primary forces sculpting the surface of an entire world.