Four coolants, four temperatures
| Coolant | Holds at about | Good for | Watch out for |
|---|---|---|---|
| Water ice | 0 °C | Fish, seafood, produce | Melt water; the box needs a drain |
| Gel packs | Around 0 °C | Chilled food, short medical runs | Can freeze products that touch them when taken straight from a freezer |
| Dry ice | −78.5 °C | Frozen goods, long frozen shipments | Gives off carbon dioxide gas; far too cold for chilled products |
| PCM plates | A chosen temperature, for example about +5 °C | Medicines and samples with a narrow range | Must be conditioned correctly before every trip |
Water ice
Ice is cheap, available in every port and in direct contact with the product, so it cools fast. It suits large rotomolded tubs and cooler boxes. Plan for the melt water.
Gel packs
Gel packs are sealed, so the load stays dry, and they can be used many times. Let frozen packs warm for a few minutes before packing them next to products that must not freeze.
Dry ice
Dry ice is solid carbon dioxide. It turns straight into gas at −78.5 °C, so it leaves no liquid and keeps goods deeply frozen. The gas must be able to escape, so never seal dry ice in an airtight container, and ventilate vehicles and rooms. Dry ice is regulated as dangerous goods in air transport; check the rules with your carrier.
PCM plates
A phase-change material melts and freezes at a temperature chosen by its maker. While it melts it absorbs heat without changing temperature, which is why a PCM made for the 2 to 8 °C range can protect medicines without the risk of freezing them. Plates are reusable. They must be fully conditioned at the right temperature before each trip.
Matching coolant to box
- Fish tubs and cooler boxes: water ice or gel packs.
- Sample transport box: coolant packs suited to the sample temperature.
- FRP medical boxes: PCM plates matched to the required range.
- EPP folding boxes: gel packs for chilled orders.
If the trip is long or the limits are tight, consider an active box instead. Read active vs passive cold chain boxes.