Buying a polystyrene box: the right choice for food and medicines

In chilled shipping, the polystyrene box is still the standard, and for good reason. EPS (expanded polystyrene) insulates reliably, weighs next to nothing, holds its shape and is unaffected by moisture. Yet purchasing regularly goes wrong: walls too thin for the transit time, an internal size that doesn't match the load, or a lid that doesn't close properly. This guide sets out what buyers and logistics managers should look for before they buy a polystyrene box.

Wall thickness and density: the two key figures

The insulating performance of a polystyrene box depends first and foremost on the wall thickness. The thicker the wall, the more slowly heat gets in, but the larger and heavier the box becomes for the same internal size. For short transit times a thinner wall is usually enough; for longer journeys, summer shipping or sensitive loads, the thicker version pays off.

The second figure is the density of the material. A higher density makes the box more resistant to compression and slightly better at insulating. If you stack boxes or ship on pallets, make sure the box can carry the weight of the shipments above it.

Just as important: keep internal and external dimensions apart. What matters is that the load plus the gel packs fit inside without much residual air. Air in the box shortens the holding time, because it circulates with every movement and spreads heat.

Polystyrene box with lid: it all comes down to the closure

A polystyrene box with lid is only as good as its closure. Look for a precisely fitting lid with a rebate: it centres itself and largely seals the joint. For shipping, the lid is also fixed with tape; a loosely placed lid is guaranteed to shift in the parcel network.

For parcel shipping, a matching outer carton is also advisable. It protects the EPS from knocks, provides a neat surface for shipping labels and ensures the shipment can be handled as an ordinary parcel in the sorting centre.

Which polystyrene box for which use?

Food and fresh produce

For vegetables, fruit and chilled foods, it is usually about fridge temperature. What counts here above all is the right ratio between box size, wall thickness and gel packs. Important: pack the load pre-chilled. A polystyrene box holds temperature, it doesn't create cold; warm products stay warm.

Meat and fish

With meat and fish, moisture comes into play: condensation and meltwater must not weaken the packaging. EPS absorbs virtually no water and is therefore well suited to this application. Additionally, pack the products tightly in film or bags so no liquid escapes, and for frozen products allow for enough frozen gel packs or dry ice — the latter strictly according to the carrier's regulations.

Medicines and lab samples

In the pharmaceutical field, the requirements are tighter: many preparations must stay between 2 and 8 °C without interruption, and deviations upwards and downwards are equally critical. What counts here is not the maximum holding time but consistency. Work with conditioned gel packs (not deep-frozen directly against the products, otherwise freeze damage looms), a fixed packing sequence, and validate the combination of box, packs and packing scheme with a data logger before it goes into the regular process.

Insulated polystyrene box: how long does it stay cold?

The most frequently asked question, and the only honest answer is: it depends on the total combination. Depending on the set-up, an insulated polystyrene box can stay within the target range from one day to several days. The decisive factors:

• Wall thickness: thicker wall, longer holding time.
• Gel packs: quantity, starting temperature and distribution in the box.
• Pre-chilling: pre-chill the products and, if possible, the box itself.
• Fill level: little residual air, fill voids with packing material.
• Outside temperature: a summer day in the delivery van demands considerably more than winter shipping.

Don't rely on general promises. Do a test shipment with a temperature logger over the actual route, including a weekend or public holiday scenario if that can occur for you. Only then do you know whether the chosen combination holds up.

Common purchasing mistakes

• Choosing a box that's too big: residual air shortens the holding time and costs freight space.
• Not allowing for the gel packs: the internal size must accommodate load and packs, not just the load.
• Looking only at the unit price: storage volume, freight and the damage from spoiled products belong in the calculation.
• Packing warm products: the box holds temperature, including the wrong one.
• No test with a logger: if you have never measured your own route, you don't know what the box really does.

Not sure which size or wall thickness suits your products? Request a sample and test the box under real conditions. In our web shop you will find polystyrene boxes with lids in various sizes, with matching gel packs.