The most common reason an ice pack swells is plain physics: fresh water grows by about 9 percent in volume as it turns to ice. USGS uses this to explain why ice floats, and notes that density shifts with dissolved substances, so brine fillings behave slightly differently. If the filling has no room for the extra volume, the pressure lands on the shell. That is why packs and plates are never filled to the brim; an expansion allowance is left inside.
| Sign | Likely cause | What to do |
|---|---|---|
| Bulges at every freeze, recovers on thawing | Overfilled, too little expansion room | On a refillable type, bring the level down to the fill line; leave a sealed plate alone |
| Stays swollen after thawing | Shell permanently deformed | Take it out of use |
| Seam or cap separating | Impact or heat | Take it out of use, check for contact with the load |
| Leak, odour or colour change | Shell opened or contents changed | Separate the pack and any load it touched |
On refillable packs the level goes up to the fill line marked on the shell. A few percent more water buys only a few percent more cooling time, yet it strains the shell at every freeze and shortens its life. Sealed plates are never topped up or drained; the ice-pack filling guide explains why a refillable model's own instructions come first.
Freezing without swelling
GEBHARDT eutectic plates have a food-safe polyethylene shell and a non-toxic brine filling. GEBHARDT's preparation rule is to freeze the plates at least 5 °C below their melting temperature, with an air gap between them so cold air can circulate, and not to use them until the filling has fully solidified. Packs crammed on top of each other in a freezer freeze late and press on one another; a freezer rack prevents both.
What to do with a swollen pack
A pack that does not regain its shape after thawing no longer sits properly in its holder, presses on the product and its packaging, and is close to puncturing, so it is withdrawn. Do not puncture it, vent it, or try to reshape it by heating or pressing. A deformed shell is strained even more on the next freeze and can crack inside the freezer.
Send your supplier photos of the label, the bulged surface and the cap or seam area, together with the conditions the pack was frozen under. If it leaks, separating the goods it touched is a step of its own. Keeping the finding, the affected product and the action taken under one incident record matches the corrective-action step in the FAO guidance.
