Keeping cool - anything, anywhere For keeping drinks, food or medicines cool longer in your passive hard or soft cooler. Just place the Freez'Pack® units in the refrigerator between 2 and 4 hours before using, until it is completely frozen. Then, insert it into a passive cooler. Not to be used in thermo-electric coolers. Food-safe (non-toxic refrigerant). Dishwasherproof. Reusable. Large size