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How To Make A Cooler Colder

Want your drinks and snacks to stay cold longer without forking over hundreds for a high-end cooler? Here's how to hack a cheap model.

Loading a cooler on boat

Photo: Thinkstockphotos.com/Jupiterimages

Until I got my latest boat, I'd never owned a boat with a fridge. I'd always used a cooler. It was OK and it fit nicely on the boat, but the performance was far from stellar. The ice melted within a day, and I thought that this was just the way it had to be. Then a couple of years back, manufacturers started to come out with what can only be described as "supercoolers" that, even in 90-degree daytime temperatures, could retain ice for days on end. These are fantastic products, but at $200-plus, way outside my budget, so I looked for a way to upgrade my existing cooler.

Tip: For best results, use spray foam recommended for filling large gaps. Some cans have an R-value printed on the side. The higher the R-value, the better the insulation.

By and large, the more insulation that a cooler has, the better it will perform. The insulation serves two masters: It keeps the heat out and keeps the cold in. I therefore figured that given the right materials, it should be more than possible to upgrade the basic cooler I already owned.

On further investigation, it turned out that many cheap coolers are just an inner and outer skin of plastic with an air space between them. If this space can be filled with some sort of insulation, rather than just relying on dead air, the contents of the cooler will stay cold far longer. To check if your cooler has only an air space between the inner and outer skins, open the lid and try to squeeze the inner and outer sides between your thumb and forefinger. Another way to tell is to tap the outer case with a knuckle. It will sound hollow if there's nothing in there apart from air.

Before undertaking this project, be sure to read and follow the spray-foam manufacturer's directions, taking note of recommended temperature and humidity ranges. Always wear protective equipment, including gloves, face mask/respirator, and eyewear.

Here's how to upgrade yours.

Tech Support

Degree Of Difficulty: Easy

Tools and Materials:

  • Drill
  • Knife
  • Tape measure
  • Spray-foam insulation (I used Great Stuff Big Gap Filler)

Time: 1 hour.

Cost: $10 plus the cost of the cooler.

Drilling holes in cooler

1. With the lid removed, drill a series of half-inch holes around the top rim of the cooler, placing them them about 4 or 5 inches apart. The spacing isn't critical, but aim for neatness. These holes are used to inject the foam and allow trapped air to escape. When the job is complete and the lid replaced, the holes will be covered by the lid.

Inserting foam in each hole in cooler

2. Insert the dispensing tube from the foam can into each hole in turn and fill until the space is about 50 percent full. The foam will expand in every direction. If you overfill, the pressure of the expanding foam will distort the cooler and may burst the sides apart. Wait a few minutes, and if the foam does not start to come out of the holes, add a little extra. Depending on the size of your cooler, you will need one to two cans.

Drill some holes in the underside of the lid and repeat the procedure. The lid is far smaller, so be careful not to overfill. You'll need a lot less foam than you did for the walls of the cooler.

Using a knife to trim excess foam

3. After leaving the foam to fully cure overnight (sometimes up to 24 hours), use a sharp knife to trim flush any excess that has squeezed out of the holes.

4. Screw the lid back on the cooler. Add ice and drinks and enjoy!

Standing The Test Of Time

Although far from scientific, I measured how long it took a 5-pound bag of ice to melt, both pre- and post insulation. With no extra insulation, the ice melted to almost nothing within four hours when the cooler with the ice inside was placed outdoors in the shade on an 80-degree day. After adding the insulation, there was still some ice left a day and half later — a dramatic and marked improvement! In use, I found that with the hacked cooler kept in the shade in the interior of the boat, a bag of ice lasts for a three- or four-day cruise, whereas previously, I'd be adding ice every day.

Mark Corke

A marine surveyor, and holder of RYA Yachtmaster Ocean certification, Mark has built five boats himself — power and sail. He was senior editor of Sail magazine's hands-on "Boatworks" publication, worked for the BBC, written four DIY books, skippered two round-the-world yachts, and holds the Guinness World Record for the fastest there-and-back crossing of the English Channel, in a kayak! He and his wife have a Grand Banks 32.