How long does dry ice last? Sublimation, moisture & replenishment in international pharma shipments

Dry ice is a time-limited refrigerant. It does not cool indefinitely — it continuously sublimates into CO₂ gas and eventually is simply gone. For a pharma shipment, the decisive question is therefore not “how cold?” but: how long will the dry ice hold up — and what happens when it runs out?

On international lanes with transhipments, customs and long dwell times, that is precisely where shipments tip over. This article explains the hold time, the often-misunderstood topic of moisture, and why replenishment at the gateway on long transports is not a luxury but a must.

How long does dry ice last — and what does it depend on?

There is no blanket figure in hours. The sublimation rate — i.e. how quickly the dry ice “disappears” — is driven by four factors:

1. Quality of the box

A vacuum-insulated box (VIP, e.g. va-Q-tec, Sofrigam) holds the cold significantly longer than a simple EPS polystyrene box. With the same amount of dry ice, the difference can be a factor of 2 or more.

2. Quantity and form

More mass lasts longer — but form matters: blocks sublimate more slowly than pellets, because they have less surface area per kilogram. Pellets cool down faster but are used up sooner.

3. Ambient temperature

The warmer the surroundings, the faster the sublimation. A container sitting in summer sun on the apron loses its dry ice noticeably faster than one in an air-conditioned warehouse.

4. How often the box is opened

Every opening lets in warm air and accelerates the loss. With customs inspections or repacking, this adds up quickly.

The moisture misconception

Unlike water ice, dry ice leaves no liquid residue — it turns to gas. The goods therefore stay dry, which is a real advantage. Still, three moisture and material effects tend to be underestimated in practice:

What goes wrong on international transports

It is not distance that kills the shipment, but the dwell times in between. This is exactly where most international dry ice shipments come off the rails:

• Differing carrier limits: every airline has its own dry ice limits per package and aircraft. What one carrier accepts, the next will reject.
• Multimodal handovers: truck → air freight → truck. Every handover is a potential dwell time — and an opening/inspection point.
• Customs, weekends, public holidays: a shipment stuck at the customs gateway on Friday evening waits until Monday in the worst case. The dry ice does not wait.
• Time zones & gateway operating hours: miss one tight connection and 30 h of planned transit turn into 50 h of real dwell time.

Replenishment: topping up dry ice at the gateway

Replenishment means: the dry ice is topped up at defined points along the route — typically at air freight gateways — before it runs out. For shipments over 24–48 h of transit, this is practically always required.

What matters

• The handler at the gateway must actually offer a dry ice top-up service — not every handler does.
• After topping up, the dry ice quantity changes — for air freight, the package must be reweighed and re-declared (UN1845 quantity on the Air Waybill).
• The top-up point belongs in the route plan before transport starts — not as a last resort once the logger is already alarming.

Checklist: international dry ice pharma shipment

Pharma manufacturers should demand these six points from their forwarder before any dry ice shipment goes abroad:

Conclusion

How long dry ice lasts is not a fixed number, but the result of box, quantity, environment and handling. On short lanes, a good box with a sufficient fill is enough. But as soon as borders, transhipments and dwell times come into play, a planned replenishment decides between success and total loss.

Anyone shipping frozen pharma internationally needs a partner who knows the hold times, plans the top-up points and monitors the shipment live — instead of hoping that “it will be fine”.