Overstuffing your freezer can put you at risk of more than being hit with a falling carton of ice cream. When a freezer is too full, the air vent may become blocked, preventing the air from circulating properly and keeping everything chilled at the same temperature. But if the freezer is almost empty, all the cold will escape when you open the door. Ideally, a freezer should be 75 percent full. If you’re short on frozen foods these days, don’t bother going on a shopping spree. Just toss in a couple of bags of ice.