Passive, thermoelectric or compressor: which cool box?

A passive box only slows the loss of cold you put in, a thermoelectric box cools a stated number of degrees below whatever the air is doing, and a compressor box holds a temperature you set. They sit next to each other in the same aisle and answer three different questions.

The passive box

No power, no moving parts, and performance that comes from foam thickness, a sealing gasket and how often the lid is lifted. Makers publish an ice retention figure in days, and that figure is measured with their own fill ratio, ambient temperature and lid discipline. Read the conditions or the number means nothing — a retention figure quoted with no ambient temperature beside it is not a measurement.

It is the lightest of the three when empty, the only one that works with no electricity at all, and the one whose performance you can genuinely change by how you pack it.

The thermoelectric box

Runs from 12 V and cools by a stated number of degrees below ambient. That phrasing is the whole specification: it is a relative claim, not a temperature. It draws current for as long as it is plugged in, and it will not reach fridge conditions in a hot car whatever the listing photograph implies.

Its case is a long weekend with vehicle power available, where you want drinks cool rather than food held cold.

The compressor box

Holds a set temperature whatever the ambient, will freeze if asked, weighs and costs the most. It publishes a consumption figure and a battery protection cut-off, and that cut-off is what decides whether it can flatten a vehicle overnight. Where the setting is adjustable, it is the single most useful control on the box.

Capacity is not what it looks like

All three are quoted in litres, and a litre of stated volume is not a litre of bottles. Check the internal depth against the tallest thing you carry — a two-litre bottle standing up rules out a surprising number of boxes — and remember the empty weight before any ice goes in, because a full box has to be carried to the pitch by somebody.

The details that decide the week

A drain plug you can reach without lifting the box onto a table. A gasket sold as a spare part, since the seal is what fails first and what quietly halves retention when it hardens. Latches that stay flexible in the cold. And on powered boxes, whether the lead supplied fits the socket you actually have.

How to decide

Work backwards from power. No power at all means passive, and then the question is foam thickness and how disciplined you are with the lid. Vehicle power for a weekend, with cool rather than cold as the goal, points at thermoelectric. Food that has to be held at a temperature, or a trip long enough that ice resupply becomes the trip’s organising principle, points at a compressor box and at reading its consumption figure carefully.

We compare box type, stated capacity in litres, insulation type and thickness, published ice retention with its stated conditions, power supply and stated consumption, battery protection settings, drain and gasket, and empty weight. The one thing worth writing down before you shop is which of those three questions you are actually asking.