What Is Dry Ice? A Plain-Language Guide

Last verified: October 6, 2026. Dry ice is the solid form of carbon dioxide, the same gas that people exhale and that makes drinks fizzy. At ordinary air pressure it does not melt into a liquid the way water ice does. Instead it goes straight from a solid to a gas, a process called sublimation, which is why it leaves no puddle and is called “dry.” It is extremely cold, far colder than a household freezer and much colder than ordinary ice, which is what makes it useful: it can hold samples, foods, and materials at very low temperatures for hours or days without electricity or a mechanical freezer.

That combination of intense cold and no liquid residue explains most of its uses, and the same properties explain most of its cautions. Because it is so cold, direct contact can injure skin. Because it turns into gas, a closed container can build pressure, and a closed room can accumulate carbon dioxide. Dry ice is therefore both an everyday laboratory and shipping material and one that deserves a clear understanding of its basic behavior.

Who Uses Dry Ice, and Why

• Research laboratories use it to keep biological samples frozen during transport between buildings or institutions, to snap-freeze small samples, and to chill baths for certain chemical procedures.
• Clinical and diagnostic laboratories use it to ship specimens that must remain frozen from collection to testing.
• Pharmaceutical and biotechnology organizations use it for moving temperature-sensitive materials, including some vaccines and biologic products, through the supply chain.
• Food industry and catering use it for keeping frozen items cold during delivery and for visual effects.
• Cleaning and maintenance applications use dry ice pellets as a blasting medium that leaves no wet residue.
• Teaching and demonstrations, where its behavior illustrates phase changes and gas properties.

Common Forms of Dry Ice

Blocks and slabs

Large blocks sublimate more slowly because they have less surface area for their mass. They are the usual choice for keeping a shipment cold over a longer period.

Pellets

Small rice-sized pellets are easy to pour around samples in a shipping box and to use for chilling, but their large surface area means they sublimate faster.

Flakes and crushed pieces

Crushed or flaked dry ice can be mixed with a liquid in a cooling bath or used to surround small items. It is convenient but short-lived.

Cut sheets and shaped pieces

Some suppliers sell pieces cut to fit particular containers, which reduces empty space and slows loss.

How Dry Ice Differs From Adjacent Materials

• Dry ice vs. water ice. Water ice melts to liquid water and is only as cold as the freezing point of water. Dry ice is much colder and leaves no liquid, so it suits samples that must stay frozen and dry.
• Dry ice vs. liquid nitrogen. Liquid nitrogen is colder still and is a liquid, used for long-term storage and rapid freezing. It requires special containers and handling. Dry ice is easier to obtain and carry, but it does not reach those temperatures and it does not last as long without resupply.
• Dry ice vs. gel packs. Gel packs hold a modest temperature suited to refrigerated shipments. They do not keep material frozen the way dry ice does.
• Dry ice vs. a mechanical freezer. A freezer maintains temperature indefinitely with power. Dry ice is a temporary, power-free solution that must be replenished.

General Cautions

This section describes widely recognized hazards in general terms. It is not a safety procedure, and the controlling rules are those of your institution, your shipper, and the supplier.

• Cold injury. Touching dry ice with bare skin can cause injury similar to a burn. People handling it typically use insulated gloves or tongs, and eye protection is commonly worn. See what laboratory PPE is for the broader category.
• Pressure. As dry ice turns to gas, it expands greatly. A tightly sealed container can build pressure and burst, so containers for dry ice are designed to vent. A sealed bottle or tube with dry ice in it can be dangerous.
• Ventilation. Carbon dioxide is heavier than air and can accumulate in small, enclosed, or poorly ventilated spaces such as cold rooms, walk-in freezers, vehicles, and elevators. In high concentrations it can displace oxygen and cause impairment. Dry ice is normally stored and used only where there is adequate ventilation.
• Storage. Dry ice is kept in an insulated container that allows gas to escape, not in an airtight one or in a standard freezer, which can be damaged by the cold and by the gas.
• Disposal. Dry ice is allowed to sublimate in a well-ventilated area rather than being thrown in a sink or trash, where it can damage plumbing or create hazards.

Common Misconceptions

Several beliefs about dry ice cause trouble in practice. One is that it is just very cold ice and can be handled the same way. It cannot, because its temperature is low enough to injure skin on contact and because it behaves as a gas source, not a liquid one. Another is that a sealed cooler is the best way to keep it. The opposite is true: a cooler that cannot vent is a pressure hazard, and shipping packages are designed to let gas out. A third is that dry ice will keep a shipment cold for as long as needed. It is a consumable coolant with a limited lifetime, and delays, warm vehicles, or thin insulation shorten that time a great deal. A fourth is that it is safe to leave in a cold room or walk-in freezer because those spaces are already cold. In fact those are small, poorly ventilated spaces where carbon dioxide can accumulate. And finally, some people think the fog that billows from dry ice is the gas itself. The visible fog is mostly water vapor from the surrounding air condensing in the cold, while carbon dioxide gas itself is invisible. Dry ice should be treated with respect, but with a clear understanding of what it is, not with fear.

Practical Notes for Research-Administration and Lab-Management Readers

• Shipping rules apply. Dry ice is regulated as a hazardous material when shipped, and carriers have requirements for packaging, labeling, and quantity. Staff who ship samples on dry ice normally need training and should follow the carrier’s and the institution’s procedures.
• Plan for resupply. Dry ice sublimates continuously, so a shipment or storage plan has to account for time and for how much is needed to last. Delays in transit are a leading cause of thawed shipments.
• Supply logistics. Many institutions rely on a supplier for regular delivery, because dry ice cannot be stockpiled for long. Planning around delivery schedules avoids shortages.
• Sample integrity. Some materials are damaged by temperature swings. For these, the choice between dry ice, liquid nitrogen, and a freezer should be driven by what the sample needs. Equipment that holds a set temperature with power, such as an incubator or a water bath, solves a different problem from dry ice.
• Training and signage. Rooms where dry ice is stored or used should have clear guidance, and everyone who handles it should know the general hazards.

This page is general information, not clinical or safety training. Follow your institution’s procedures, the supplier’s and carrier’s requirements, and the manufacturer’s instructions for any specific container or use.

The Short Version

Dry ice is solid carbon dioxide that sublimates directly to gas and is far colder than water ice. That makes it valuable for transporting and briefly storing frozen samples without power, but it can injure skin, build pressure in sealed containers, and displace oxygen in poorly ventilated spaces. Using it well means choosing the right form, using vented insulated containers, planning for steady loss, and following shipping and safety rules. For managers, the practical takeaway is to treat dry ice as a regulated, time-limited coolant: assign someone to order it, train people who handle it, give it a ventilated place to be stored, and write down who is responsible for shipments.

Frequently Asked Questions

What is dry ice made of?

Carbon dioxide in solid form. It is the same gas that is in the air and in carbonated drinks, cooled and compressed into a solid.

Why is it called dry ice?

Because it does not melt into a liquid. It turns directly into gas, so it leaves no wet residue.

What is dry ice used for in a laboratory?

Keeping samples frozen during transport, chilling small samples or cooling baths, and shipping temperature-sensitive materials.

Can dry ice be stored in a sealed container?

No. As it turns to gas, pressure builds, and a tightly sealed container can burst. It should be kept in an insulated container that allows gas to escape.

Is dry ice dangerous?

It can be if mishandled. The main hazards are cold injury to skin, pressure buildup in closed containers, and carbon dioxide accumulating in poorly ventilated spaces. General precautions and local rules reduce those risks.

How long does dry ice last?

It depends on the amount, form, container, and surroundings. It sublimates continuously, with large blocks in well-insulated containers lasting longer than pellets in thin ones.