Large gel packs: when to choose them and what to watch out for
Anyone who ships chilled goods often thinks about the box first and the cooling second. Yet that's precisely where the biggest savings lie. Large gel packs are in many situations a better choice than a handful of small ones, but not always. This is what you need to watch for when shipping medicines, food, meat, fish, vegetables, or laboratory samples.
Why a large gel pack warms up more slowly
It's simple physics: the larger the frozen mass, the smaller the surface area in relation to the volume. A large pack therefore absorbs heat more slowly than the same weight distributed over a stack of small packs. All those small packs together have much more outer surface through which the cold leaks away.
Moreover: fewer packs means fewer handling steps when packing, less chance of forgetting one, and a more stable load in the box. One large flat pack lies flat on or under the product; ten small ones shift in all directions during transport.
Choosing large gel packs: the trade-offs
Weight counts double
Every gel pack adds to shipping weight. A larger pack cools more efficiently per kilo, so you often need less total cooling weight for the same transit time. But calculate it through: with parcel shipping you pay for that weight, and the box has to be able to handle it. Choose the cooling that matches the transit time of your shipment, nothing more.
Frozen or chilled product?
This is where things most often go wrong. A deeply frozen pack lying directly against a chilled product can freeze that product locally. For meat or fish that's usually no disaster, for fresh vegetables, fruit, or temperature-sensitive medicines it is. If you're shipping at refrigerator temperature (2 to 8 degrees), place a barrier between the pack and product: a layer of cardboard, an insulation film, or the product's own packaging. If you're shipping frozen, the pack can lie right against it.
The placement in the box
Warm air rises, cold air sinks. A gel pack on top of the product therefore works better than underneath. For longer transit times or hot days: distribute the cooling, with at least one pack at the top. And fill empty spaces. Air that can circulate in the box displaces heat; a tightly packed box holds the temperature longer.
Mistakes we often see
- Packs that aren't fully frozen. A pack that still feels liquid in the core has already lost a large part of its cooling capacity before the box closes. Freeze flat and well in advance, and check before use.
- Judging cooling without insulation. The pack does its job together with the box. A large gel pack in thin cardboard loses to a smaller pack in a good insulated polystyrene box or thermal pallet cover. Always judge the combination.
- Choosing a box that's too large. More empty space means more air to cool. A properly-sized box with a large pack performs better than a spacious box with extra packs added.
- Packing warm product. Gel packs are there to hold temperature, not to cool product back down. Product that goes into the box at room temperature eats into your cooling capacity. Pack chilled product also in a chilled state.
- Testing once and never again. Packaging that was plenty in March can fall short in July. Test under the hottest conditions in which you ship, not the average.
How you determine what's enough
There's no table that works for every shipment, because transit time, outside temperature, box contents, and product temperature differ for each shipper. What always works: a test shipment to yourself or a colleague at a distance, with a temperature logger between the product. Then you see exactly when the temperature starts to rise and whether you have margin. Do that test properly once and you'll know for the whole season what you're working with. Repeat it if the product, box size, or shipping time changes.
Start generously and scale back. It's cheaper to send one less pack after a successful test than to have a shipment rejected because the temperature ran too high.
Try first, then order
Want to know if large gel packs in your packaging make a difference? Request a sample and run a test shipment with it, or browse the selection of gel packs in our webshop. Testing with your own product and your own box tells you more than any rule of thumb.
