How long does a thermal cover keep cargo at temperature?
A thermal cover does not cool. That sounds like a detail, but it is the most important sentence in this article: the cover adds no cold, it slows the warming of your load. Anyone who understands that calculates differently.
Where the heat comes from
In air freight, the risk is not in the flight itself. The cargo hold is generally cool. The risk is in the hours before and after: the drive from the cold store to the terminal, waiting on the platform, loading and unloading. A pallet that stands in the sun for two hours picks up radiant heat on the top, and that is exactly where most heat enters.
Four factors
Starting temperature of the load. This is the biggest. Cargo that goes in at temperature stays good much longer than cargo that has already warmed up. A cover cannot repair a mistake at the start.
Outside temperature and sun or shade. The difference between a pallet in the shade and the same pallet in full sun is greater than the difference between a single-layer and a double-layer cover.
How long the pallet stands outside the chilled environment. Calculate with the longest conceivable scenario, not the average.
Mass of the load. A full, heavy pallet has a lot of thermal mass and warms up slowly. A half-full pallet with a lot of air warms up quickly.
Why we do not quote hours
You will not find a promise such as forty-eight hours in this catalogue. That would be a number without meaning, because it depends entirely on the four factors above. Anyone who does quote such a number is assuming laboratory conditions that do not exist on a platform.
What you can do
Make sure the load goes into the cover at temperature. Choose double-layer for long routes or warm climates. Add coolants in the load itself when the route is long, because the cover only slows the warming. And always cover the top, because that is where the heat enters. You will find suitable cooling elements in our collection, and the range of thermal pallet covers contains several versions.
Measure for yourself instead of guessing
The only reliable way to know your own holding time is to measure. This is how:
- Place a data logger in the middle of the load and a second one close to the outside, under the cover.
- Set the measuring interval so that you can see the curve clearly, for example every few minutes.
- Run the real route, including waiting times on the platform or the dock.
- Read out the data and look at where the temperature rises fastest. That is usually during waiting.
- Adjust the set-up, for example with an extra layer or more cooling elements, and measure again.
You can find data loggers in the collection data loggers. One measurement says something about your situation at that moment. Repeat the test in a warmer or colder period if your route runs all year round.
Situations compared
- Short journey, pallet stays in the shade: the cover has little to do, the starting temperature is decisive.
- Long wait on the platform in the sun: the top receives a lot of radiation. A well-covered top and possibly double-layer help here.
- Warm climate or long route: combine cover and cooling elements in the load and measure the curve.
- Half-full pallet: there is a lot of air in it, so the load warms up faster. Fill the pallet as completely as possible.
Common mistakes
- Placing a warm load in the cover and expecting it to cool down.
- Not covering the top.
- Calculating with an average waiting time instead of the longest.
- Using a cover that does not close properly around the pallet.
Checklist before departure
- Has the load been loaded at the right temperature?
- Does the cover close all the way round and is the top covered?
- Are cooling elements needed for this route?
- Is there a data logger in the pallet?
- Does the recipient know that the pallet must be unpacked quickly?
Cover or refrigerated truck?
For short routes and transfer moments, a cover may be enough. For long routes with a strict temperature regime, you will often choose active cooling. The trade-off is covered in our article thermal cover or refrigerated truck. You can read more about the cover itself in insulating thermal pallet cover.
Frequently asked questions
Can you give a holding time in hours for my pallet?
No. Without knowing your route, your load and the outside temperature, that would be a guess. We are happy to think along with you about the set-up, and with a data logger you measure the result yourself.
Is double-layer always better?
Not always. On long routes or in warm climates, double-layer often makes sense. On short routes, single-layer may be enough. What fits depends on your situation.
What matters more: the cover or the starting temperature?
The starting temperature. A cover holds what is inside, it does not restore a warm load.
Why does the top warm up first?
On a platform or in a warehouse, radiation comes mainly from above. The sun and warm air under a roof hit the top of the pallet hardest. A cover that fully covers the top and closes properly therefore helps more than extra insulation on the sides.
Where can I find more advice?
On our page cold chain packaging for air freight you can read more about packing for air cargo. Or get in touch with us with your route, and we will think along with you.
