Plastic recycling is complex, and the question of which plastics “cannot be recycled” often causes confusion. The Resin Identification Code (RIC) system, the number inside the chasing arrows symbol, was created to help facilities sort materials, but consumers frequently mistake it as a universal guarantee of recyclability. An item may be technically recyclable in a laboratory setting but practically unrecyclable within the standard municipal system due to its chemical makeup, physical form, or local market economics. For most people, an item is unrecyclable if it is not accepted in the curbside bin, which depends on factors beyond the material’s basic polymer type.
The Chemical Classifications That Are Rarely Recycled
The plastics chemically incompatible with the dominant recycling streams of Polyethylene Terephthalate (PET, RIC 1) and High-Density Polyethylene (HDPE, RIC 2) are typically rejected due to contamination risk. Polyvinyl Chloride (PVC), labeled as RIC 3, is a prime example because it contains chlorine atoms. When PVC is melted at the high temperatures used for other plastics, it releases hydrochloric acid gas, which is highly corrosive to recycling equipment and can destroy an entire batch of valuable material. This chemical incompatibility is compounded by toxic additives, such as plasticizers and heavy metals, used to give PVC its final properties, making uniform reprocessing nearly impossible.
Polystyrene (RIC 6)
Polystyrene (PS), marked as RIC 6, presents a different chemical barrier tied to its physical state. When used as expanded foam (Styrofoam), it is over 95% air, making it extremely bulky and uneconomical to transport for mechanical recycling. The low density means the cost of shipping a full truckload outweighs the low market value of the resulting recycled resin.
RIC 7 Plastics
Plastics labeled with RIC 7, or “Other,” represent a mix of polymers or multi-material plastics that are chemically diverse. Since different polymers have different melting points, attempting to melt them together results in a weak, unstable, and low-quality final material. Economically separating these varied chemical structures is often prohibitively complex and expensive for standard facilities.
Format and Contamination Barriers to Recycling
Many plastics chemically suitable for recycling are rejected at Material Recovery Facilities (MRFs) because of their physical form or contamination level. Flexible plastic film, bags, and wraps, often made from Low-Density Polyethylene (LDPE, RIC 4), are notorious for wrapping around the rotating shafts and disc screens of sorting machinery. These “tanglers” necessitate frequent shutdowns for manual removal, increasing operational costs and facility downtime.
Items too small to be efficiently separated by automated equipment are also routinely discarded. Any plastic item under approximately two to three inches, such as loose bottle caps or small containers, tends to fall through the screens designed to filter out fine contaminants. These small pieces are then routed into the general waste stream.
Multi-layer packaging, such as pouches for snacks or pet food, is functionally impossible for most MRFs to process. These items combine several different materials—like plastic, aluminum foil, and paper—fused together to create high-performance barriers. Since mechanical recycling cannot economically separate these fused layers into pure, single-material streams, the entire composite item is rejected. Contamination from food residue, grease, or chemicals is also a pervasive issue, as it degrades the quality of the recycled resin, making the final product unusable for new manufacturing applications.
Infrastructure and Economic Limitations
The ultimate fate of a recyclable plastic is heavily influenced by the infrastructure and economic realities of the local market. MRFs are businesses, and they only invest in sorting equipment for materials that have a consistent and profitable end market. If there is no reliable buyer for a specific recycled polymer, such as Polypropylene (PP, RIC 5) or Polystyrene (RIC 6), the MRF has little incentive to process it, regardless of technical recyclability.
This economic viability is fragile and constantly threatened by the price of virgin plastic, which is tied to the fluctuating cost of crude oil. When oil prices are low, virgin plastic can be significantly cheaper to produce than the cost of collecting, sorting, and reprocessing recycled resin. This disparity undermines the competitiveness of the recycling industry.
The sorting technology available at a facility also creates a systemic barrier. Many older or smaller MRFs lack the advanced optical sorters and specialized machinery needed to efficiently separate all seven RIC types. These facilities often focus only on high-value materials like PET and HDPE bottles, which have the most established markets. Consequently, what is accepted in a curbside bin varies significantly by location, reflecting localized infrastructure, available end markets, and the cost of investing in new equipment.