Gel packs vs dry ice: which does your shipment need?
The choice is not a preference — it is set by how cold the product must stay. Gel packs are a phase-change coolant that melts at 0 °C, so they hold a product in the refrigerated band (roughly 2–8 °C). Dry ice is frozen carbon dioxide at −78 °C, so it is the only practical way to keep a product frozen through transit. If your product must stay frozen, gel packs cannot do it; if it only needs to stay cool, dry ice is overkill and adds shipping restrictions.
How much do you need?
The honest amount comes from heat-leak physics, not a rule of thumb like “half the payload weight.” Heat enters the box through its surface, driven by the temperature gap and slowed by the insulation — heat ≈ area × temperature gap × hours ÷ R-value. Divide that heat by the coolant’s latent heat (about 246 BTU per pound for subliming dry ice, about 144 BTU per pound for a melting water-based gel pack) to get the mass you need. The calculator does this from your box size, foam thickness, temperatures, and transit time.
The trade-offs beyond the math
- Dry ice keeps things frozen and sublimates to gas (no meltwater), but it is a regulated dangerous good for air freight: by air, up to 2.5 kg (5.5 lb) per package is excepted from most rules if the box is vented and marked “Dry ice” with the contents and the net weight of dry ice; above that it ships as Class 9, UN1845, with full marking, labeling, documentation and carrier arrangements (49 CFR 173.217).
- Gel packs are unregulated, reusable, and leave no residue, but they cannot hold sub-freezing temperatures and are heavier for the same cooling.
- Insulation matters more than coolant — doubling the R-value roughly halves the coolant you need. Spend on the box before you spend on ice.
Questions
How much dry ice do I need to ship frozen food?
Enough to absorb the heat leaking into the box over the transit time. That depends on box surface area, insulation R-value, the ambient-to-target temperature gap, and hours in transit — not a fixed fraction of payload weight. The calculator estimates it from those inputs; as a sanity check, a well-insulated small box for an overnight often needs a few pounds, but a hot, long, or thin-walled shipment needs far more.
Can gel packs keep food frozen?
No. Gel packs are water-based and melt at 0 °C, so they hold a refrigerated band (about 2–8 °C) but cannot keep a product frozen. To ship something frozen you need dry ice (−78 °C) or a phase-change material rated below freezing. This is physics, not brand preference.
How long do gel packs last in shipping?
As long as it takes the leaking heat to melt them — a function of how many you pack, the insulation, and the temperature gap. More packs and thicker foam extend it. The calculator converts your shipment into a gel-pack count for the transit time you enter; add margin for delays and hot weather.
Is dry ice or are gel packs cheaper to ship?
It depends on the target temperature and service. Gel packs are unregulated and simple but heavier and can’t freeze; dry ice cools more per pound and leaves no meltwater but is a regulated dangerous good for air, with labeling and venting rules. For refrigerated goods, gel packs usually win on total cost; for frozen goods, dry ice is the only option.
Does better insulation reduce how much coolant I need?
Yes, substantially. Coolant scales inversely with the insulation R-value, so doubling the foam roughly halves the dry ice or gel packs required. Insulation is usually the cheaper lever — improve the box before adding more coolant.
Labels that survive the cold.
PackOS doesn’t sell insulated shippers or coolant. Quick Quote prices custom roll labels today — if your cold-chain product needs one, upload the artwork for an instant label quote and check the adhesive and facestock it selects against your storage temperature.