How many ice packs does your cooler need?

The Cooler Shock sizing chart

We built this chart from the way our hard case ice packs perform in typical hard-sided coolers. Each pack is 13" x 10" x 1.4" and weighs about 5 lbs filled, and it does the cooling work of roughly 7 lbs of loose ice.

Screw-top pouches follow the same logic. A large 14" x 10" pouch replaces 5 to 6 lbs of ice, so count it like a hard pack. Two mid-size 10" x 10" packs or three small 8.5" x 7.5" packs add up to about one hard pack.

Why fewer, bigger packs hold cold longer

Cold lasts as long as there is frozen mass left to absorb heat. A large pack has more frozen mass relative to its surface, so it gives up its cold more slowly than a handful of small ice cubes. That is why a block of ice outlasts cubed ice, and why a 5 lb hard pack outlasts a bag of cubes of the same weight.

Our packs add a second advantage: the cooling mix freezes at 18°F rather than 32°F. The pack starts colder than ice and spends longer below the temperature where food starts to warm. In practice, a size-matched cooler with our packs stays cold for 24 to 48 hours.

Where to put the packs

Cold air sinks and warm air comes in from the top every time the lid opens. The best layout we have found:

• One pack flat on the floor, under the food that needs the most cold — meat, dairy, anything raw.
• One pack standing against the back wall, the side that usually faces the sun.
• One pack laid across the top of the load, where the warm air hits first.
• Drinks in the middle, where they are easy to grab without moving the packs.

On a 32 quart cooler, three packs in that layout keep food cold through a long weekend. On a 48 quart, add a fourth pack on the opposite wall.

Mixing ice packs and ice on long trips

For trips longer than two days, many of our owners run packs and a smaller amount of ice together. The packs handle the long, steady cold at the bottom of the cooler. A bag of cubes on top chills warm drinks fast and fills the gaps between cans. You will use roughly half the ice you used to, and what does melt sits above the food instead of drowning it.

If you use a rotomolded cooler, pre-chill it the night before with a sacrificial bag of ice or a spare frozen pack. A cooler that starts warm spends the first hours cooling its own walls instead of your food.

Choosing between reusable ice packs

Reusable ice packs come in two broad types. Hard case ice packs carry the most frozen mass and stay cold the longest; they are the alternative to block ice. Slim, soft ice packs take less space and fit where a hard shell cannot; they are the alternative to cubed ice in a sandwich bag. The difference matters when you count: one hard pack covers what two small ice packs would.

Material makes a difference too. Our hard cases are HDPE and polycarbonate; our pouches are nylon-reinforced and durable enough for years of refreezable use. Both have the same freezing point of 18°F, so the cold you get from each pound of pack is the same — the question is simply what shape fits your cooler and your lunch boxes.

If you are testing a new set, run it once at home first: freeze the packs for a full day, load the cooler the way you would on a trip, and check the temperature of the food after a few hours. That small test tells you whether to add one more ice pack before the long weekend.

Lunch bags and soft coolers

Soft coolers hold cold for less time than hard ones, so size up. For a lunch bag, two small packs — one under the food and one on top — work better than one big pack. For a soft cooler of 20 to 30 cans, use two large pouches or two prefilled medium packs, and keep the bag in the shade.

Quick sizing answers