The two types of foam also hold different types of gas: Open-cell bubbles are often filled with water vapor, while closed-cell foams are filled with a variety of other chemicals with better insulating properties, such as pentane. (For decades, most insulating closed-cell foams were filled with CFCs; those were phased out after their impact on the ozone layer was discovered.
In addition, if the lid of your cooler features cup holders, consider putting a plug made of insulating material like styrofoam at the bottom of them. (Or, if you don't use them, consider filling them up with spray foam or memory foam!
Open-cell foam is more flexible and lighter-weight, but because most of the gas bubbles are in contact with each other, it's easier for heat to travel through it and is therefore less insulating.
Second, the polymer molecules that make up the walls of the bubbles are bonded fairly loosely; this limits the rate at which heat can be transferred from one molecule to another. (Molecules in high heat-conducting materials like metal contain free-flowing electrons, which transfer heat more readily than their less mobile counterparts.
The generally accepted ratio of ice to contents is about 2:1. (The ideal ratio has so many factors, including the specific heat of your contents, that it’s not something worth calculating before each camping trip. ) The melting rate of ice is directly related to its surface area: A block of ice melts much slower than an equivalent amount of ice in small cubes.
Every time the contents of your cooler come into contact with the warmer air outside, those faster-moving molecules get in there and poke your cold molecules in the ribs, making them move faster—and making your beer a little warmer.
It’s still insulating your cooler's contents. (Water may conduct heat better than air, but as long as the water is colder than the air, it's the better choice to keep your beer in.
Do not, we repeat, DO NOT drain the ice water out of your cooler. And keep that thing closed! https://t.co/dSWY9xwNaF— WIRED (@WIRED) July 3, 2019