A parcel sent by courier does not travel in one vehicle from the origin branch to the destination branch. One or more sorting hubs sit in between; there the parcel moves along belts, is sorted and waits for the next vehicle. The delivery time does not show that wait separately. So the packaging is chosen not for a two-day journey but for two days plus an uncertain wait.
Ask the carrier before shipping
How many hubs can the parcel pass through, can it sit at a branch over the weekend, and who tells the recipient about a delay? For a shipment leaving after Thursday, count on a weekend wait. If you use dry ice, get the carrier's acceptance conditions in writing.
A worked example of the time
Example: quoted service 2 days, shipment leaves Thursday at 16:00. The times below are example values, not measurements; ask the carrier for the real ones.
| Step | Example time | Running total |
|---|---|---|
| Origin branch to sorting hub | 12 hours | 12 hours |
| Waiting at the hub until the next vehicle | 36 hours | 48 hours |
| From the hub to the delivery vehicle and the door | 12 hours | 60 hours |
The total is 12 + 36 + 12 = 60 hours, so a parcel leaving Thursday at 16:00 arrives on Sunday at 04:00. If the quoted time is 48 hours, the 12-hour gap belongs to the plan, not to the packaging, and the packaging should be chosen for 60 hours. Choose the profile length by the waiting time as well: in this example the 72-hour profile looks sufficient, but if the weekend wait stretches to 96 hours, the 144-hour profile is needed.
Packaging faces two separate tests
On belts and in stacks a thin-walled box is crushed, and a crushed box loses its insulation. For that reason mechanical strength and thermal performance are tested together on the same pack. If the pack has to stay upright, achieve that through the shape of the packaging rather than the orientation arrow; the label is not always read in automatic sorting.
For the mechanical side, ISTA 3A applies: individual packages of 150 lb (70 kg) or less shipped by parcel system, by air or by ground. For the thermal side there is the ISTA 7E profile set: heat and cold profiles built from data measured in 82 different lanes across summer and winter campaigns. ISTA's Thermal Lane Data Package also includes 72-hour and 144-hour formatted versions of them.
The ISTA test page calls 7E a development test, while the 7E profile document says the profiles are general simulations and do not represent the worst-case exposure. So run your own trial on the longest and most transfer-heavy route.
If dry ice is used
For dry ice (UN 1845) sent by air, IATA Packing Instruction 954 requires packaging that lets the carbon dioxide gas escape, so that pressure does not build up and rupture the pack. The net dry ice weight is marked on the outside of the package, and arrangements are made with the operator for each shipment. The instruction allows up to 200 kg per package; each airline's own loading limit also applies.
Place recorders close to the product in a few representative shipments . At arrival, read the temperature curve and the total time; if something went wrong, match it to the carrier's transfer records to see at which hub. Run the trial to the farthest address with the most transfers: a pack that holds there can reasonably be expected to hold on the shorter routes.
If the delivery window cannot meet the target temperature, more cold source is not the only answer. Replan the service, the route or the way of delivery.
