How long a soft cooler really holds ice

What the number describes

Cold retention figures assume a full bag, contents that were already cold when they went in, ice distributed through the load rather than sitting on top, and a lid that stays shut. Under those conditions our cooler bodies hold temperature for up to sixteen hours — pack at seven in the morning and the last drinks are still cold after dark. Change any one of those assumptions and the number moves.

The four things that cost you hours

Air is the enemy: a half-empty cooler holds warm air that the ice then has to chill, so fill the gaps with towels or extra bottles. Warm contents spend the first two hours stealing cold from the ice instead of the other way round. Direct sun on a dark shell can add ten degrees to the outside of the bag. And every opening dumps the cold air out of the bottom — on a long day, decide who is the designated opener.

Cubes, blocks or packs

Cubes chill fastest because they touch everything; blocks last longest because they melt slowly; ice packs are the tidiest and the only sensible choice in a lunch bag. The practical answer for a day out is both — a block at the bottom for endurance and cubes poured around the drinks for contact. Salt in the ice water drops the temperature further, but it also makes a mess of anything unsealed.

Why melt water is not a failure

A cooler full of ice water is still a working cooler — water at zero degrees is a better conductor than air, and drinks sitting in it chill faster than drinks resting on cubes. Our liners are heat-pressed precisely so you can leave that water in the bag until you get home. Drain it, wipe the inside, leave the cooler open to dry, and fold it flat once it is dry.