The public often uses the terms Styrofoam and polystyrene interchangeably to describe the lightweight, foamy material found in coffee cups and shipping packages. This common usage overlooks important distinctions between the generic chemical material and a specific, branded product. Polystyrene refers to the base polymer, a type of plastic, while STYROFOAM™ is a trademarked name for a specialized foam product. These differences govern how the materials are manufactured, what they are used for, and how they interact with the environment.
The Definitive Answer: Brand Name vs. Generic Term
The confusion between Styrofoam and polystyrene stems from a common phenomenon where a brand name becomes the default term for an entire category of products. Polystyrene is the generic name for a synthetic plastic polymer, chemically known as poly(phenyl ethene). It is a hydrocarbon polymer created by linking together thousands of styrene monomers.
STYROFOAM™ is a registered trademark owned by the DuPont company. The trademark specifically applies to a type of extruded polystyrene foam used almost exclusively for building insulation. The disposable cups and packaging materials most people call “Styrofoam” are actually Expanded Polystyrene (EPS), which is not the trademarked product.
Polystyrene: The Base Polymer and Its Forms
Polystyrene (PS) is a versatile, transparent, and rigid plastic resin produced in the millions of tons each year. This thermoplastic polymer is a solid at room temperature, but it can be melted and reshaped multiple times without significant degradation.
PS is formed into several distinct products, including solid General Purpose Polystyrene (GPPS) used for items like disposable cutlery and CD cases. The most common foamed version is Expanded Polystyrene (EPS), the white, beaded material found in coolers and protective packaging. EPS foam is manufactured by treating small polystyrene beads with steam, causing them to expand and fuse together into a lightweight, closed-cell structure. Because this foam is composed of approximately 95% to 98% air, it possesses buoyancy and insulating properties.
STYROFOAM™: Extruded Polystyrene and Its Unique Purpose
The material sold under the STYROFOAM™ brand is technically Extruded Polystyrene (XPS) foam. The manufacturing process for XPS is distinctly different from EPS; instead of expanding beads with steam, a molten polystyrene mixture is forced through a die, or extruded. This extrusion process creates a material with a continuous, uniform, and smooth closed-cell structure.
XPS is notably denser and more resistant to moisture absorption than EPS. This superior moisture resistance, combined with a high compressive strength, makes it ideal for construction applications. XPS is used as rigid insulation boards for walls, roofs, and foundations, often appearing in distinctive colors such as blue or pink. The closed-cell composition provides a high thermal resistance value, making it a highly effective thermal barrier in energy-efficient construction.
Recycling and Environmental Considerations
All forms of polystyrene—solid, EPS, and XPS—are assigned the Resin Identification Code #6, indicating they are chemically the same type of plastic. However, recycling them presents significant challenges due to physical properties and contamination issues.
Challenges to Recycling
The extremely lightweight and bulky nature of EPS foam, which is mostly air, makes it uneconomical to transport for mechanical recycling compared to other plastics. Contamination is also a major hurdle, as EPS food containers are often soiled with food residue, oils, and other substances that can ruin an entire batch of clean material. While the base polymer is recyclable, the lack of local infrastructure and the need for specialized equipment to densify the material mean most municipal curbside programs do not accept it. The environmental persistence of polystyrene is also a concern, as it is non-biodegradable and can break down into microplastic particles that pose a threat to wildlife and ecosystems.