Plastic Numbers: Breaking Down Recycling Codes

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

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 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.

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.

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.

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.

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.