I imagine most of you have gone around and bought drinks from a nearby store. Maybe you’re out on your morning jog, and you felt a bit thirsty; perhaps you’re out on a trip with friends, and you’re looking for something refreshing to keep the fun going. Thanks to the marvels of modern-day materials science, we can now enjoy the convenience of having our favorite drinks anytime, anywhere—all thanks to the engineering innovations made in their packaging. But then you turn the bottle over its head, and notice a strange marking on its bottom. Perhaps you see a number, surrounded by a triangle. What’s that all about?

The Resin Identification Codes (RIC)

The Resin Identification Codes, or RIC for short, are a series of designations given to the types of plastic used in common consumer items and materials, also known as commodity plastics. If a specific item (or perhaps a part of it) is made of a certain class of plastic, these numbers would let you know. Common materials for plastics are often branded with one of seven different number classifications.

1. Poly(ethylene terephthalate)

Named PET for short, these are perhaps the most famous of the plastics. While in the context of fabrics, they’re mostly known as polyesters, it’s food packaging that gave this class of plastics their fame (or notoriety); it’s the “PET” in “PET bottle.” These plastics are lightweight, and can be easily recyclable due to their inherent properties, hence their ubiquity and general usefulness.

2. High-density polyethylene

Shortened to HDPE, these plastics are used for their high strength-to-density ratio; it’s resistant to breaking when you make it thick enough, so it’s mostly used for situations where you really don’t want the stuff inside spilling out: milk containers, bottle caps, jerry cans, trash cans, and the like.

3. Poly(vinyl chloride)

PVC for short, these plastics are known for their excellent chemical resistance. You can throw acids, bases, alcohols, salt solutions, and pretty much any other common liquid waste on it and PVC still won’t budge—hence why it’s famously used as pipe material for domestic sewage systems.

4. Low-density polyethylene

LDPE, as the name suggests, is yet another grade of polyethylene, much like HDPE. However, due to how it’s made compared to its denser counterpart, it’s very light and flexible, allowing the formation of items and materials that can bend or contort in basic use without failure. This is why LDPE is the most common material used in plastic bags. As you might have guessed, the base plastic polyethylene (which it shares with HDPE, #2) is also the most-produced plastic in the world.

5. Polypropylene

Being the least dense of the commodity plastics, PP is often used for when you need the properties of a plastic without much of the mass that accompanies it. As such, it’s mostly used for lightweight reinforcement in the industry, such as car bumpers, fiber filler in composites, and others. It can also be used in food packaging—mostly for takeout drink cups.

6. Polystyrene

PS for short, this is a type of plastic that shares a lot of its properties with the other plastics on this list, hence why you’ll also see it on some food packaging, as well as plastic cutlery, among other items. It is, however, famous for one of the ways it can be formed; it can be foamed into a material filled with air pockets, which makes it ideal for impact absorption; this is why you’ll mostly recognize PS from old packaging of electronics and similarly fragile items, as well as packing peanuts. (Nowadays, manufacturers use biodegradable alternatives to help in the environmental effort—hence why you rarely see PS foam when you buy a new smartphone.)

7. Others

The 7th code functions as a catch-all for the rest of the commodity plastics not in the other six categories: polycarbonates (PC), for engineering applications; polyamides (PA), perhaps most known by one of its variants, Nylon; and bioplastics, among others. You’ll find these in various machines and implementations, from cars to computers and appliances.

Now, if you’ll remember, these triangles used to have arrows on them, too—much like the famous recycling symbol. New revisions to the convention implemented by the American Society for Testing Materials (ASTM) have removed these arrows. As it turns out, the arrows became a tad bit misleading; instead of informing everyday consumers of what plastic it was, they were instead being used as rough metrics of how recyclable it was as an item. Seeing the numbers inside a recycling symbol gave off the impression that the item was just that much recyclable. Of course, this was a total misunderstanding, but consumers didn’t know it; to help avoid these misconceptions, the ASTM decided to remove the arrows entirely back in 2013 with a revision to the ASTM standard D7611, and have since left them as standard triangles.

Cap It All Off

While yes, it’s not always pretty to think about the implications and widespread environmental impact of manufacturing these conveniences, their impact on our everyday lives is undeniable. Computers, body transplants, candy bar wrappers—they’re all there.

Of course, with efforts underway to help limit how much plastic we use and waste, it is imperative that we as consumers know just what exactly we are buying with our money. From proper waste disposal to recycling efforts that help return some of the waste plastic back into the manufacturing process, it’s important to know what these plastics actually are. Not only does it inform us of what it’s used for; it also helps waste disposal and recycling facilities determine what exactly they need to do to handle the waste once it reaches their hands. (Now you know why most recycling facilities recommend that you remove bottle caps from PET bottles; they’re made of different plastics, and are thus recycled in different ways.)

So, yes, that’s precisely what the numbers under your soda bottle are for: it helps inform you, and it helps inform the people who handle it after you throw it at the nearest proper disposal area. But with increasing public awareness about how we use and misuse our generated plastic, some have made it their mission to help out in our collective recycling and/or proper waste disposal efforts as best as they can.

Bibliography

• The Editors. (2018, April 23). WHICH PLASTICS ARE RECYCLABLE BY NUMBER? The Old Farmer’s Almanac. Retrieved September 8, 2021, from https://www.almanac.com/content/which-plastics-are-recyclable-number
• Identifying Recyclable Resources. (n.d.). Recycle.co.nz. Retrieved September 8, 2021, from https://www.recycle.co.nz/symbols.php
• Plastics News. (2013, June 11). Say so long to recycling code arrows. Plastics News. Retrieved September 8, 2021, from https://www.plasticsnews.com/article/20130611/NEWS/130619978/say-so-long-to-recycling-code-arrows
• ASTM D7611 / D7611M-20, Standard Practice for Coding Plastic Manufactured Articles for Resin Identification, ASTM International, West Conshohocken, PA, 2020, www.astm.org