PS Foam Resin Identification

Foam 101

Polystyrene, typically marked with the #6 resin identification code, which is used to identify plastic types for recycling purposes, is a thermoplastic found in rigid and foam applications.

Often confused with Styrofoam™, a registered trademark of Dow Chemical Company’s insulation, polystyrene foam is used in a variety of ways across multiple industries, including automotive, foodservice and packaging. The #6 symbol is seen on cups and plates, protective transportation packaging, and even egg cartons. In fact, due to their positive life cycle attributes, functionality, and low cost, polystyrene foam products are a sensible choice for many organizations. 

How It’s Made

Foam is created through polymerization. More specifically, it is formed through the process of addition polymerization, causing monomers—or groups of atoms—to link together into chains. These chains are called polymers, also known generically as plastics. The polymers are converted into finished products like medical coolers, transportation packaging, and foodservice items through a variety of processing methods.

It’s important to note that foam foodservice products are manufactured without chlorofluorocarbons (CFCs)[1] or any other ozone-depleting chemicals. In fact, a voluntary 1988[2] agreement ensured that manufacturers switched to other EPA-approved chemicals, reducing the ozone-depletion potential of foodservice packaging by more than 95 percent.


Polystyrene beads are heated to expand, making them easier to mold into the desired shape. Once molded, they are cooled by circulating water through them or by spraying water on their exterior. 

[1] Alexander, J. H. (1993). In Defense of Garbage. Westport, CT: Praeger Publishers.

[2] Foodservice Packaging Institute. (2012). Foodservice Packaging and…The Ozone Layer.

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