How long does a polystyrene foam box stay cold?

Short answer: in practice, a polystyrene box keeps products at temperature for 12 to 48 hours. A thin-walled box with two gel packs achieves 8–12 hours, a thick-walled one with four gel packs 36–48 hours, and with dry ice the contents remain frozen for 48–72 hours. The range is wide because cooling duration depends on several factors at the same time.

What does the cooling duration depend on?

Four factors together determine how long an Polystyrene Box stays cold:

• Wall thickness. The thicker the wall, the longer the insulation performs. A thick-walled box (30–50 mm) maintains the temperature roughly two to three times longer than a thin-walled one (20 mm).
• Number and weight of the gel packs. More cooling mass means longer cooling. Two 400-gram packs are the standard; for longer routes, choose 600 or 1000 grams, or additional packs.
• Outside temperature. Indicative times apply at around 20 °C. On a hot summer day of 30 °C, the cooling duration can easily be a third shorter.
• Fill level. Empty space is warm air. A tightly packed box cools for significantly longer than a half-empty one.

Indicative times from practice

The values below come from practical tests with our own boxes at an outside temperature of around 20 °C:

• Thin-walled (20 mm) with 2 gel packs: 8–12 hours
• Thick-walled (40 mm) with 2 gel packs: 24–36 hours
• Thick-walled (40 mm) with 4 gel packs: 36–48 hours
• Thick-walled (50 mm) with dry ice: 48–72 hours (frozen)

How to extend the cooling duration

With a few simple measures, you can get extra hours out of the same box:

• Place gel packs on top of the product. Cold air sinks and cools the entire contents evenly.
• Freeze the gel packs for at least 24 hours before using them, so they are completely frozen through.
• Pre-cool the product itself. The gel packs then only need to maintain the temperature, not cool the product down first.
• Fill empty space with void fill material or additional gel packs.
• Choose the right size. A smaller box that is full is preferable to a large one that leaves half empty.

Shipping frozen goods? Use dry ice

For frozen products, combine a thick-walled Polystyrene Box with dry ice (-78 °C). This keeps the contents frozen for a full 48 to 72 hours — long enough for international shipments. Please note your carrier’s shipping rules for dry ice.

Want certainty for your route?

Every shipping route is different. If you want to know exactly what happens in your situation, order a data logger and measure your route. Or view all standard sizes in our range of Polystyrene Boxes directly — manufactured in-house in the Netherlands and delivered within 2 working days.