Expanded Polystyrene (EPS), commonly referred to as Styrofoam, is a lightweight plastic foam used extensively for packaging, insulation, and food service items. This material is made from polystyrene resin, designated as Plastic Identification Code 6. Although the resin is a thermoplastic polymer and technically capable of being recycled, its physical form creates significant logistical challenges for standard municipal recycling systems. The process of recycling this foam requires specialized industrial equipment and dedicated collection pathways, moving it outside the typical curbside collection framework.
Why Polystyrene is Difficult to Recycle
The primary obstacle to recycling expanded polystyrene (EPS) is its extremely low density, which makes transportation economically unfeasible for most recyclers. EPS foam is composed of about 98% trapped air, meaning that a large volume of the material contains very little actual plastic by weight. This low density translates to high costs for shipping and storing the material, as trucks quickly fill up by volume rather than by weight. The material’s tendency to crumble easily also leads to small fragments that contaminate other valuable recyclable streams during collection and sorting.
Contamination is another major barrier, especially for foam used in food service applications. Food residue, dirt, liquid, or adhesive tape drastically reduce the quality of the resulting recycled resin. Because the foam is porous, consumers find it difficult to clean thoroughly enough to meet the strict standards required for industrial recycling. Processors often reject contaminated batches to protect the quality of the final product, adding complexity to the process.
The Industrial Recycling Process
The specialized industrial process for recycling expanded polystyrene focuses on reducing the material’s volume to make it manageable. This process begins with a rigorous sorting and preparation stage at the specialized facility. Workers confirm the material is clean, dry, and free from non-polystyrene contaminants like film plastic or tape before it is fed into a pre-shredder or crusher to break the bulky foam into smaller, uniform fragments.
The next step is densification, which drastically reduces the air content and volume using specialized machinery called densifiers or compactors. Mechanical densifiers compress the shredded foam into dense blocks, achieving a volume reduction of up to 50:1, making the material compact enough for cost-effective transport. Thermal densifiers are often more efficient, using heat and pressure to melt the foam, creating a solid, uniform mass called an ingot, which can achieve volume reduction ratios as high as 90:1.
The solid ingots or compressed blocks are then ready for the final transformation into a usable raw material. This involves feeding the dense material into an extruder, which applies high heat and mechanical shear to melt the polystyrene into a liquid resin. The molten plastic is pushed through a filtration system to remove any remaining impurities that survived the initial cleaning and densification stages.
This filtered, melted polymer is forced through a die to form continuous strands. As these strands cool and solidify, they are cut into small, uniform pellets by a pelletizer. These recycled polystyrene (rPS) pellets are the final commodity, ready to be sold to manufacturers as a high-density, easily transportable raw material.
Consumer Access and Advanced Pathways
Since EPS is generally not accepted in curbside bins, consumers must use alternative collection methods to get the material to a specialized recycler. The most common pathway involves dedicated drop-off centers run by local governments, private recycling companies, or retail stores. Some organizations also offer mail-back programs, allowing consumers to ship clean, pre-prepared foam directly to a processing facility.
Once the rPS pellets are created, they are used to manufacture a wide variety of new products, reducing the demand for virgin plastic resin. Applications include durable goods like picture frames, crown molding, insulation board for construction, and new protective packaging materials. Increased demand for recycled content is driving greater investment in the infrastructure needed to support these specialized recycling processes.
Beyond the mechanical process, advanced pathways like chemical recycling are being developed to handle more contaminated or mixed polystyrene waste streams. Chemical recycling, such as depolymerization, breaks the plastic polymer down into its original building block, the styrene monomer. This process allows for the creation of a purified raw material that is virtually identical to virgin styrene, enabling a circular economy for polystyrene, even for material that mechanical processes cannot handle.