Plastic Numbers: Breaking Down Recycling Codes

By: Melanie Radzicki McManus & Desiree Bowie  | 
bottom of pill bottle
The bottom of this pill bottle shows that it is made of No. 5 plastic, which means it is made of polypropylene and usually can be recycled. Marilyn Root/Getty Images

Plastics aren't great for the environment or our health. Unfortunately for everyone, a lot of consumer goods are enclosed in the stuff. On the plus side, many plastics are recyclable, which is helpful because plastics can take up to 1,000 years to decompose in a landfill.

Most plastics contain a recycling symbol formed from arrows, often placed at the bottom of the item, to help you figure out whether or not you've got a recyclable item. And, as there are seven categories of plastics, a number from one to seven is set inside the triangle to tell you which kind of plastic you've got.


Let's take a closer look at these code numbers — also known as plastic numbers — and what they mean.

Categories of Plastic

First, we'll explore the seven categories of plastic and their characteristics [source: Seaman]:

  • 1: Polyethylene terephthalate (often abbreviated as PET or PETE)
  • 2: High-density polyethylene (HDPE)
  • 3: Polyvinyl chloride (PVC)
  • 4: Low-density polyethylene (LDPE)
  • 5: Polypropylene (PP)
  • 6: Polystyrene (PS)
  • 7: Other
No. 1 Plastics

PETE are used for items such as plastic soda bottles, large plastic containers, water cooler bottles and cooking oil containers. It's the most common type of plastic and is meant for single use, rather than reuse.


No. 2 Plastics

HDPE typically contain liquids such as milk, cleaning fluids, laundry detergent and shampoo.

No. 3 Plastics

PVC is the base for any form of vinyl, from siding to seat covers. It was once commonly used to make trays that hold fruit and sweets and food wrap (like cling and aluminum foil). However, due to concerns about plasticizers (like phthalates) potentially leaching into food, many manufacturers are switching to other materials for food wrap, especially those intended for microwave use.

No. 4 Plastics

Plastic shopping bags and cling wraps are made from low-density polythene (LDPE).

No. 5 Plastics

Polypropylene (PP) is used in furniture, luggage, pill bottles, toys and plastic linings for diapers, cereal and yogurt cups.

No. 6 Plastics

Polystyrene (PS) is also used in toys, as well as in Styrofoam cups, takeout containers and hard packing.

No. 7 Plastics

Finally, this last one is a catch-all category for all other plastics, such as acrylic, nylon, baby bottles and fiberglass.


The Plastic Coding System

The code numbers on plastic items, often found inside a triangle of arrows (resembling a recycling symbol), represent the resin identification code (RIC). The RIC system was introduced in 1988 by the Society of the Plastics Industry (now known as the Plastics Industry Association) in the United States.

Resin identification codes help identify the type of plastic resin from which a product is made, which is essential for recycling as different plastics have different recycling processes and compatibilities.


Are Certain Types of Plastic Safer Than Others?

Some plastic types are safer than others, especially when considering their applications, potential for chemical leaching and environmental impact. Factors such as temperature, exposure to UV light and the type of food or drink they contain (e.g., acidic, fatty) can all influence the safety of a particular plastic in specific uses.

  1. Polyethylene terephthalate (PET) - Code #1: Primarily used for bottled beverages, PET plastic has been deemed safe for single use. However, potential concerns arise with leaching of antimony, especially when exposed to high temperatures or over prolonged periods.
  2. High-density polyethylene (HDPE) - Code #2: Found in milk jugs, detergent bottles, shampoo bottles and some toys, HDPE plastic is renowned for its safety and low risk of leaching.
  3. Polyvinyl chloride (PVC) - Code #3: Found in some toys, shower curtains, plastic food wrap and other items, PVC plastic can contain phthalates or softening agents with potential health risks. Additionally, the manufacturing or incineration of PVC can release harmful chemicals into the environment.
  4. Low-density polyethylene (LDPE) - Code #4: Typically used for plastic bags and some plastic bottles, this type of plastic is recognized as safe with minimal leaching risk.
  5. Polypropylene (PP) - Code #5: Commonly used in yogurt containers, straws and baby bottles, PP plastic is heat-resistant and generally considered safe for food storage.
  6. Polystyrene (PS) - Code #6: This type of plastic is used in items like takeout containers, egg cartons and Styrofoam cups. There's potential for leaching styrene, which can be a neurotoxin and possible human carcinogen, especially when subjected to heat.
  7. Other (various) - Code #7: This umbrella category for various types of plastics includes polycarbonate, known to release BPA (bisphenol A). BPA has been scrutinized due to potential hormonal effects, prompting a shift toward BPA-free products by many manufacturers.

Note that the safety of plastics can also depend on their specific use and treatment. For instance, a plastic container might be safe for cold storage but not for microwave use. Always consult manufacturer guidelines and recommendations to ensure safe usage.


Recycling Plastic

There are several key things to know about recycling plastic. First, No. 7 plastics — the ones in the "other" category — are a mix of recyclable and nonrecyclable products. Unless you're a plastics expert, you won't be able to tell the difference, so it's best to avoid recycling these products [source: Anderson].

Second, you can only recycle clean plastic, meaning you must wash items before tossing them in your recycling bin.


Third, even if you have an item that is clean and recyclable, it won't necessarily be recycled. Municipalities often set local recycling regulations, so check your city website to see which plastics are accepted. Some plastics that are not accepted for curbside pickup may be accepted at special recycling sites.

Finally, if a product doesn't have a recycling symbol, toss it in the trash. It's better to keep a potential contaminant out of the recycling stream than take a chance.


Recycling Compostable Plastics

There are a few unique challenges and misconceptions with regard to the recycling process for compostable plastics. Often mistaken for traditional plastics, compostable variants are designed to degrade under specific composting conditions rather than be recycled. When mixed with conventional recyclables, they can contaminate the recycling stream, compromising the quality of recycled materials.

Contrary to what the term "compostable" might suggest, these plastics don't readily break down in regular home composts or natural environments. Their intended destination is industrial composting facilities, where optimal conditions enable decomposition within months.


However, such facilities aren't universally accessible. The public's confusion between biodegradable, compostable and recyclable plastics highlights the need for clearer labeling and education.

Ultimately, the net environmental impact of compostable plastic depends on proper disposal and the availability of suitable composting facilities.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.


Lots More Information

Related Articles
More Great Links

  • Barrett, Mike. "The Numbers on Plastic Bottles: What do Plastic Recycling Symbols Mean?" Natural Society. Feb. 6, 2013. (Jan. 30, 2019)
  • LeBlanc, Rick. "The Decomposition of Waste in Landfills: A Story of Time and Materials." The Balance Small Business. Dec. 16, 2018. (Jan. 30, 2019)
  • Ryan, Sheryl. "Which Plastics Can or Cannot Go In The Recycle Bin? Here's Your Quick List." Greenopedia. (Jan. 30, 2019)
  • Seaman, Greg. "Plastics by the Numbers." EarthEasy. May 2, 2012. (Jan. 30, 2019)
  • Sedaghat, Lillygol. "7 Things You Didn't Know About Plastic (and Recycling). National Geographic. April 4, 2018. (Jan. 30, 2019)