The short version: nine to fourteen days is normal, the pack is spent within two, and the solid does not mind.
A single-use temperature data logger costs a few pounds and converts speculation into a record. If the temperature history matters to you, buy one rather than arguing about packaging.
What a cold pack actually holds, and for how long
| Packing | Ambient | Time below 10 °C | What that means on a 12-day lane |
|---|
| One phase-change pack, thin-walled box | 25 °C | 1–2 days | At ambient for roughly ten of the twelve |
| One phase-change pack, thin-walled box | 35 °C | under 1 day | At ambient for essentially the whole lane |
| Two packs, insulated liner | 25 °C | 2–3 days | Buys a day; does not change the conclusion |
| Lyophilised solid, no pack | 25 °C | not applicable | Dry powder is chemically stable at ambient |
| Anything in solution | 25 °C | not applicable | A different risk entirely; hydrolysis proceeds |
A liquefied pack on arrival is the expected outcome rather than evidence of a problem. A single-use logger, not a heavier pack, is what turns this from speculation into a record.
Tracking quality is the more informative signal: continuous scanning at every hop indicates a real logistics chain, and a tracking number that goes dark for a week indicates something else.
Customs and legal considerations are separate from thermal ones and are the more consequential risk in most jurisdictions.
Buy a data logger if the temperature history genuinely matters to you.
5Adding a vote because this deserves more of them. – two_two_micron 10 months ago add a comment