How to Distinguish Between Different Kinds of Plastic


Plastic is a versatile material that comes in many different shapes. This articles provides an overview about what different kinds of plastic exist and how they are delineated. 

Article Highlights

  • SPI codes are the most important classification for plastics.
  • Plastic is distinguished by its chemical structure and density.
  • Only some are commonly known such as PET for bottles (Polyethylene Terephthalate).

Plastic is a collective term used for a wide range of synthetic products or semi-synthetic materials. They are found everywhere from the clothes we wear to the cars we travel in. The word ‘’plastic’’ comes from the Greek word ”plastikos” which means fit for molding, whilst ”plastos” meaning molded which refers to the material’s malleability. It is not a pure substance but rather a mix of it, with the high polymer (or synthetic resin) as its main component and an addition of auxiliary materials such as fillers, plasticizers, lubricants, stabilizers, coloring agents, and etc. improves its quality. In 1988, the Society of the Plastics Industry (SPI) established an organized system which uses SPI codes on each plastic product. This is to help both consumers and recyclers to properly recycle and dispose of each type of plastic based on its chemical components.


plastic spi categories
An Overview about the different plastic categories


SPI code of 1 are plastic that are made with polyethylene terephthalate which is also known as PET or PETE. A PETE-based container absorbs both the odors and flavors from foods and drinks that are stored inside of them. Products of this plastic are water bottles of all sizes, jars for common kitchen goods such as peanut butter, and many more. When recycled, these materials can be used for either clothing materials or carpets.

SPI code of 2 are high-density polyethylene, or HDPE products. It is known to be safe, due its ability to prevent leakage of chemicals into either foods or drinks.  Products made from this plastic would include milk jugs, laundry detergent, shampoos and conditioners, and soap bottles. When these are recycled, they can be used for plastic lumber or bathroom partition materials.

SPI code of 3 is made with polyvinyl chloride. It is usually found in plumbing pipes and flooring tiles. It is never to be used for food items due its harmful effects when ingested. But when recycled, it can be used for flooring, walls, and industrial-grade materials.

SPI code of 4 is made with low-density polyethylene, or LDPE which is known for its flexibility and durability. It is a safe choice for food storage such as Ziploc sandwich bags. These aren’t commonly recycled but are still viable to be used as garbage can material and other common household products.

SPI code of 5 is made with polypropylene. It is durable and can withstand high temperatures which are best used in products such as Tupperware’s, prescription bottles, etc. These aren’t usually recycled but can be reused as durable items like rakes.

SPI code of 6 is made with polystyrene, also known as Styrofoam. Products would include disposable coffee cups, refrigerator trays, cosmetic bags, etc. Recycled Styrofoam can be used for license plate frames and ruler.

Lastly, SPI code of 7 is used for miscellaneous types of plastic that are not classified by the other 6. This would include Polycarbonate and polylactide. Polycarbonate is commonly used in baby bottles, large water bottles, and etc.


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