Dry ice — solid carbon dioxide at around -78.5°C — is the standard way to keep shipments at ultra-low temperatures in transit. It's effective and widely used, but it's also classified as a dangerous good, which means shipping it comes with specific rules that are easy to get wrong if you haven't shipped it before.
Why dry ice, specifically
Unlike wet ice or gel packs, dry ice sublimates directly from solid to gas rather than melting, which means no liquid runoff to manage and a much colder sustained temperature — making it the standard choice for vaccines, biological samples and other material that needs to stay well below freezing throughout transit.
The rule that catches people out: sublimation
Dry ice doesn't melt — it sublimates, turning directly into CO₂ gas. That has two practical consequences. First, the quantity you pack decreases steadily over the journey, so shipments need enough dry ice at the start to still have some left at the estimated arrival time, with a margin for delays. Second, that CO₂ gas needs somewhere to go: packaging must allow it to vent, because a fully sealed container can build dangerous pressure.
Why it's a regulated dangerous good
Dry ice is classified as UN1845, Class 9 (miscellaneous dangerous goods) under IATA and international transport regulations, primarily because of the CO₂ gas released as it sublimates — in an enclosed space like an aircraft hold, that gas needs to be accounted for. This means:
- Shipments have a maximum permitted quantity per package, set by the carrier and the transport mode.
- Packages require correct hazard labeling (the Class 9 diamond) and the net weight of dry ice marked clearly on the outside.
- Shipping documentation must declare the dry ice as a dangerous good, separate from any declaration for the biological material itself.
- Airlines apply their own limits on top of the general regulations, and these vary by carrier and aircraft type.
Calculating how much you need
The right quantity depends on the insulated container's performance, the ambient temperature the shipment will pass through, and the total transit time including realistic delays — not just the scheduled flight or drive time. Under-packing is the most common failure mode: a shipment that runs out of dry ice a few hours before arrival has effectively broken its cold chain, even if everything else was done correctly.
How we handle it
We calculate dry ice quantities against the actual route and realistic transit times, and handle the dangerous goods documentation and labeling that comes with it. If your shipment needs dry ice and you want the logistics side handled properly, that's exactly what we do.