Styrofoam, a common trade name for expanded polystyrene (EPS) foam, is widely recognized for its ability to maintain temperature stability. It does not actively generate heat, but it is highly effective at slowing the rate at which thermal energy moves. This ability to resist temperature change makes it a preferred material for keeping hot items hot and cold items cold for extended periods.
What Defines Polystyrene Foam
The foam commonly called Styrofoam is technically Expanded Polystyrene (EPS), a rigid and remarkably lightweight material. It is created by taking tiny beads of solid polystyrene plastic and expanding them with heat, usually using a blowing agent like pentane. This process causes the beads to inflate and fuse together into a solid, closed-cell foam matrix. The resulting material is composed of approximately 98% trapped air and only 2% plastic, giving it a low density and high insulating potential.
The Three Methods of Heat Transfer
To understand how any material insulates, it is necessary to grasp the three ways heat energy moves. Conduction is the transfer of heat through direct contact between materials, such as when a metal spoon heats up in a hot cup of soup. Convection involves the transfer of energy through the circulation of fluids, like gases or liquids, such as hot air rising above a radiator. Radiation is the transfer of heat energy through electromagnetic waves that do not require a medium, such as the warmth felt from sunlight.
How Trapped Air Prevents Temperature Change
The exceptional insulating capability of expanded polystyrene stems directly from its structure and the nature of the air trapped within it. Air is inherently a poor conductor of heat, and since EPS is almost entirely air, its thermal conductivity is very low. The closed-cell formation encapsulates this air within tiny pockets, which prevents the air from circulating freely. This structural design is what effectively minimizes convective heat transfer.
The solid polystyrene matrix itself is also a poor thermal conductor, reducing the amount of heat that can pass through the material via direct contact (conduction). Because the trapped air cannot circulate, it cannot form convection currents that would carry heat away from a hot beverage or into a cold item. The combination of a low-conductivity solid and immobilized air allows the material to act as a highly effective barrier against the movement of heat energy, stabilizing the temperature of its contents.
Common Uses and Material Limitations
Expanded polystyrene is commonly used in applications where temperature maintenance is desired, such as disposable coffee cups, picnic coolers, and insulated shipping containers for food and medical supplies. Its lightweight nature and resistance to moisture make it highly practical for these uses. In construction, it is also used as rigid foam insulation for walls, roofs, and foundations to improve building energy efficiency.
Material Limitations
While effective, the material does have limits. It has a relatively lower thermal resistance value (R-value) compared to some denser foam insulators. Prolonged exposure to ultraviolet light, such as direct sunlight, can cause the material to degrade over time. Although EPS has low water absorption, if water penetrates the foam, it can reduce the material’s insulating performance.