An ice pack is specified by two variables, and neither is size. The first is how long the shipment has to hold its temperature band; the second is whether the pack may touch the food. A larger pack answers neither — it is more weight on the freight bill, and if it is colder than the product can tolerate it is a problem, not a solution. This guide separates the forms, sets out what each is for, and gives a table for matching pack to transit.
1. Three forms, three different jobs
- Water ice. Changes phase at 0 °C, carries a large amount of latent heat for its cost, and melts into free liquid. Effective for keeping something cold; messy if it leaks.
- Gel packs. Water held in a gel so the melt stays in place. Usually formulated to freeze a few degrees below zero, reusable, and no free liquid if the outer film holds.
- Phase-change sheets. Formulated to change phase at a chosen temperature rather than at 0 °C. This is the form that holds a chilled band — around 2 to 8 °C — instead of driving the shipment towards freezing.
The third is the distinction that matters. Keeping something cold and holding it at a temperature are not the same objective, and only one form is designed for the second.
2. Duration and contact are the two variables
- Duration sets the mass and the form. Short trips can be served by water ice; long ones need either a phase-change product or a much better box.
- Contact sets the material. Some gel formulations are made in food-contact grades and some are not. Where the pack may touch the product, that is a specification to confirm rather than assume.
- The box sets the requirement, not the other way round. A well-insulated box with less coolant outperforms a poor box with more, because most of the coolant's capacity goes on compensating for heat through the walls.
So the quantity is not chosen from product weight alone. It follows from the box, the ambient temperature and the duration, and is confirmed by a test run rather than a formula.
3. Choosing by transit duration
| Transit duration | Form direction | How to estimate quantity | Direct food contact | Insulated box |
|---|---|---|---|---|
| Under 12 hours | water ice, or a light gel pack | start from a coolant-to-product ratio, then confirm on a test run | water ice in a sealed food-grade bag is usual | a basic liner usually suffices; the box is not the limit |
| 12 to 24 hours | gel packs, for the melt containment | the ratio rises; box quality starts to dominate | confirm the gel grade if it may touch the product | wall thickness matters more than coolant mass |
| 24 to 48 hours | phase-change sheets, to hold a band rather than to chill | sized against the box's measured performance, not product weight | keep the coolant separated from the product | the box is the primary specification here |
| Over 48 hours | phase-change plus a high-performance box, or a different mode | test-run data is the only reliable basis | separation is standard practice | coolant alone will not carry this duration |
Directions rather than figures, because ambient temperature, box construction and product thermal mass all move the answer by more than any table captures. Where the shipment also needs liquid managed inside the pack — melt water, exudate or both — that is a separate product: seafood absorbent pad covers the seafood case, the wider range sits under fresh absorbent pads, and the family itself under cold-chain ice packs.
4. Where ice pack specifications go wrong
- Buying on size. Mass is not duration. What matters is phase-change behaviour, the box and the ambient temperature.
- Using a freezer pack for a chilled shipment. A pack at −18 °C drives a chilled product towards freezing — a different kind of damage from warming up.
- Assuming any gel may touch food. Formulations differ. If the pack can contact the product, confirm the grade rather than assuming it.
- Specifying coolant before the box. The box decides how much of the coolant's capacity is available to the product at all.
FAQ
Is a bigger ice pack better?
Not by itself. It adds weight and freight cost, and does not extend duration as reliably as a better box. Size is the last variable, not the first.
What is the difference between a gel pack and water ice?
Containment of the melt. Water ice turns into free liquid; a gel holds it in place, so a leak is a smaller event and the pack can be reused.
Can ice packs touch food directly?
Only where the formulation is made in a food-contact grade. Water ice in a sealed food-grade bag is the common route; for gels, confirm the grade.
How do I work out how many I need?
Start from the box's performance, the ambient temperature and the duration, then confirm with a test run. A ratio from product weight alone is a starting point, not an answer.
Browse the range
Start from the ice packs range, or the wider meat absorbent pads group for the packs they ship alongside. Send the transit duration, the box and the temperature band the product must hold, and a form can be matched before samples are issued.