What is popularly called a Styrofoam™ cooler is a container designed to keep food and drinks hot or cold for an extended period of time. Commonly seen at picnics, beaches and backyard barbecues, the Styrofoam™ cooler is a popular choice for those needing a cooler due to its wide availability, disposability and inexpensive price. A traditional picnic cooler can often cost many times more than a Styrofoam™ cooler.
It may surprise many to know that what is commonly known as a Styrofoam™ cooler is not actually made of Styrofoam™ at all! Styrofoam™ is a trademarked name of the Dow Chemical Company for its brand of polystyrene foam. According to the company’s website, “there isn’t a coffee cup, cooler or packaging material in the world made from Styrofoam™.” While Styrofoam™ and the material used to make the ubiquitous coolers are both made from polystyrene foam, they are actually composed of different polystyrene products.
Both polystyrene foam and hard-sided coolers work by reducing a process known as heat transfer. Whenever two objects of different temperatures come into contact with each other, heat will transfer from the warmer object to the colder object until both are the same temperature. This explains why a cold drink left outside will eventually warm up to room temperature. The heat of the surrounding environment transfers to the cold drink raising its temperature.
Essentially foam and hard-sided picnic coolers keep things hot or cold because they prevent heat from entering or leaving the container. Items which are cold are kept that way because the cooler prevents the transfer of heat into the container. Conversely, items which are hot stay hot because the cooler prevents heat from leaving.
A polystyrene foam cooler works because polystyrene foam is composed of up to eighty percent air. The molecules of air in the foam reduce the amount of heat that is allowed to pass through it. This makes polystyrene foam a poor conductor of heat. A traditional picnic cooler has a vacuum layer in between the compartment that holds the food and the exterior shell. The vacuum layer reduces the transfer of heat, keeping food and drink hot or cold. Thermal bottles work on this same principle.
Foam coolers are popular choices for many because they are inexpensive and readily available. However, polystyrene foam is easily damaged and foam coolers are not typically designed for long term use.