Foldable Thermal Box: How to Reach 48 to 72 Hours
A foldable thermal box can reach 48 to 72 hours, but not on its own. These six points determine whether you actually achieve that duration.
Choose the right number of layers
The 4-layer insulated liner is sufficient for up to about 48 hours refrigerated. For frozen goods, longer routes or high outdoor temperatures, choose 6-layer. The cardboard outer box stays the same. You will find an overview of the thermal boxes in the collection.
Freeze the coolant through completely
This is where it goes wrong most often. Lay the gel packs flat and separate in the freezer at minus 18 degrees or lower. Stacked, they feel hard but are still liquid inside, and then you only achieve half the expected duration. You can read more about this in freezing and packing ice packs.
Calculate the quantity
Rule of thumb: one 400-gram pack per 5 litres of volume for 24 hours. Double this for 48 hours or frozen goods. With a large box, distribute the packs instead of piling them in one spot. The full method is set out in how many gel packs do you need per shipment.
Place the cooling on top
Cold sinks. Packs at the bottom mainly cool the base; packs on top cool the entire contents.
Fill the box
Air is the space in which heat circulates. A full box holds its temperature considerably longer than a half-full one. Choose a smaller size that fills up instead.
Close the insulated liner
The liner must be closed before the cardboard box is closed. An open liner lets the cold escape into the space between the liner and the cardboard, and that works against you.
Plan for your longest route
Not the average. A shipment that is normally in transit for 48 hours can take 60 hours if delayed. Build in that margin, because temperature damage is irreversible.
Preparation in sequence
A fixed sequence prevents mistakes. This is how you pack a foldable thermal box:
- Freeze the gel packs through completely well in advance, flat and separate from each other.
- Pre-cool the product to the required temperature. A warm product uses up the cooling before the shipment has even left.
- Place the liner in the outer box and keep the liner open until everything is inside.
- Put the product in, with gel packs around it and on top.
- Fill empty space with packing material, so that nothing can shift.
- Close the liner and only then the cardboard box.
- Ship as soon as possible. Do not leave the box standing in a warm room for hours.
Common mistakes
- Gel packs that were not in the freezer for long enough.
- A box that is too large for the contents.
- Putting a warm product into a cooled box.
- Shipping at the end of the week, so that the parcel sits over the weekend.
- Calculating only with the average delivery time.
Mind summer and winter
In summer a parcel heats up faster, especially if it sits in a delivery van or on a doorstep. In winter, frost can be the problem for products that must not freeze. A foldable thermal box protects against both, but the set-up differs. In summer you use more gel packs. In winter you make sure the product does not lie directly against a frozen pack. So test per season with a data logger.
What the recipient needs to do
Good packaging does not help if the parcel is left standing after arrival. Ask your customer to unpack the parcel straight away and put the product immediately into the fridge or freezer. Put this as a short instruction on a card in the box. That prevents the cold chain from still breaking at the last metre.
Check with a data logger
A calculation is a starting point. Whether you really achieve 48 or 72 hours only becomes clear when you measure. For a trial shipment, put a data logger in the box and read out the temperature curve after arrival. Do the test in warm weather and on your longest route. If you reach the required duration with room to spare, you can keep the number of gel packs or layers. If you fall short, change one thing at a time and test again.
Frequently asked questions
Can I reach 72 hours with a 4-layer liner?
That depends on the outside temperature, the fill and the gel packs. According to the rule of thumb above, a 4-layer liner is sufficient for up to about 48 hours refrigerated. For longer routes, take 6-layer and test with a data logger.
Can I reuse gel packs?
Yes, provided they are intact and freeze through completely again. Check them for leaks before you use them again.
How do I distribute the gel packs?
Distribute them around the product and place some on top. A pile at the bottom mainly cools the base.
What if my shipment is delayed?
Build in a margin on your longest expected route. For extra certainty, choose 6-layer and more gel packs.
Want to know more?
You can read more about the influence of wall thickness and outside temperature in how long does a thermal cover keep the load at temperature. Unsure which combination suits your product? Send us your route and dimensions and we will help you think it through.
