The refrigerator door isn’t like regular cabinet doors. It has a piece of rubber that seals to the body when it’s shut to keep the cold air in. Often it’s magnetized so you feel resistance when you go to open it again. The trouble lies in when you overpack your fridge or overstock the shelves on the door. It may appear shut, but it doesn’t seal, letting cold air escape. Give your door a little tug once you shut it to make sure it’s closed completely.