How to pre-chill a cooler: how long, with what, and why the lab that pre-chilled got the longest numbers

Why a cooler needs pre-chilling

Foam insulates by being full of trapped air, and trapped air at 70°F is a heat reservoir. A YETI Tundra 45 is 23 lb by Yeti's figure; an RTIC 65 is 37.7 lb; a Pelican 45QW is 43.7 lb. Every one of those pounds starts the trip at room temperature (or hotter, out of a garage or a truck bed), and the ice you load has to pull all of it down to near freezing before it can do anything for the food. That is the first several pounds of ice, gone before you leave the driveway. Pre-chilling spends cheap ice at home so the expensive ice at the lake does the job you bought it for. The thicker the foam, the more this matters: a rotomolded cooler with two to three inches of insulation has more mass to cool than an Igloo with one and a half.

How long

For a trip: the night before is the practical minimum and 24 hours is the ceiling worth bothering with. For a soft cooler small enough to fit, the freezer overnight does the same job faster. A cooler that has been in a hot truck bed needs longer than one from a cool basement; put the truck-bed cooler in the shade with a hose-down first.

With what

• Sacrificial ice. A bag of cheap cubes, dumped in the morning. Simple; costs a bag.
• Frozen gallon jugs. Free, reusable, and in the morning they become block ice for the trip. The best option for most people.
• Hard ice packs. Igloo's MaxCold block and Engel's 32°F cooler packs go from the freezer into the cooler overnight and come out still frozen enough to stay in for the trip. No water, no mess. Best ice packs.
• Not dry ice. Pre-chilling with dry ice works in a rated cooler but is expensive and needs ventilation; regular ice does the job. Dry ice in a cooler.

Then load it

Dump the meltwater (this is the one time draining is right: you want to replace the water with fresh ice, not keep it). Put the pre-chill jugs or packs on the bottom as block ice. Load contents that are already cold from the refrigerator; a warm case of cans is another heat reservoir. Cubes on top and in the gaps. Fill the dead space. Shut it and keep it shut. From here the rest of the ranked list takes over: how to keep ice longer in a cooler.

Two packs for the job

Pre-chilling is step zero; the loading order is step one. How to pack a cooler covers the layers, the 2:1 ratio the makers quote their own capacities at, and why you should not drain the meltwater.