No, they contain a special phase change material which does not need cooling. However, doing so for 1 hour in the fridge will extend the time the mat stays cool by 30-45 mins. PLEASE NOTE: A very hot dog on a freezing cold mat is not a good idea. The mat is cool enough when it naturally recharges in a cool, dark room or by being placed in a fridge for no more than 1 hour. Please do not place it in the freezer.