Accepted answer
The relevant physics is that a single phase-change pack in a thin-walled box holds below ten degrees for one to two days in a twenty-five-degree ambient, and considerably less at thirty-five.
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.
Reported transit ranges with tracking
| Lane | Reported range | Median | Where the variance comes from |
|---|
| Coastal China → western Europe | 8–14 days | 11 days | Customs queue at the destination hub |
| Inland China → western Europe | 10–16 days | 13 days | Domestic leg to the international gateway |
| China → United Kingdom | 8–13 days | 10 days | Single clearance point, usually quick |
| China → United States, west | 8–16 days | 12 days | Onward domestic carrier |
| China → Australia | 10–20 days | 15 days | Fewer direct services; inspection rate |
| Regional warehouse → same region | 2–5 days | 3 days | No clearance step at all |
These are ranges members have reported, not quotes. Judge a lane on whether tracking scans continuously rather than on days elapsed.
Mechanically, asking a supplier to hold a shipment during a heatwave is a reasonable request that the better ones honour, and it costs a week rather than an order.
Phase-change pack hold times are a function of mass, latent heat and box insulation, and published figures for small parcels are on the order of a day or two.
A liquefied pack on arrival is expected. It is not evidence of a problem.