Dry ice is colder than wet ice. Plus, it doesn't melt, so you don't have to worry as much about soggy sandwiches! It's also lightweight and usually easy to find in your local grocery store. For these reasons, many people decide to add it to their freezer, especially when they know they'll be using it for at least a few days. While this can be a great and effective choice, there are some guidelines to keep in mind. First, dry ice is best suited for stainless steel or styrofoam coolers. The extreme temperature can cause damage to a plastic cooler if left for too long. That said, if you're determined to use dry ice, then add a protective styrofoam layer around the interior of your container. Simply cut pieces of styrofoam and lay them on the bottom and sides of your cooler. You can also use cardboard to achieve the same purpose. It's also important to understand that as it melts, dry ice releases a gas. This gas can be dangerous to inhale or consume, so be sure to follow these important safety precautions.