Which plastic bottle size is worst for the environment? Study reveals a surprising answer

Polyethylene terephthalate, otherwise known as PET, is as ubiquitous a material as it is unknown to most of the people who use it every day.

PET is most widely used to produce single-use water and soda bottles, the kind ubiquitous at sporting events, music festivals, and local grocery stores around the world. Although we know single-use plastic is inherently terrible for the environment, one of the biggest complaints regarding these bottles is to do with what they contain — soda.

Public-health officials want to shrink the bottles down to try and limit our consumption of such sugary, acidic beverages. But a new study published Thursday in the journal Scientific Reports points to a different problem, one that undercuts the public-health push. When it comes to these bottles, turns out the smaller the package, the greater the waste.

Here’s the background — PET bottles have been a waste problem ever since Nathaniel Wyeth invented them in 1973. The material is perfectly recyclable, and the Covid-19 pandemic has actually led to a “substantial increase” in PET recycling at facilities across the nation, according to industry publication Resource Recycling.

But those increases might not make much of a dent compared to the massive amount of PET bottles Americans waste every day. The EPA estimates the PET recycling rate to be 29.1 percent — so at least 70 percent of PET bottles go to the landfill.

Couple this to the beverage industry's embrace of the ever-diminishing bottle size, pushed on by public-health concerns over how soda rots Americans' teeth and their insides. For example: A 2020 blog post from the American Beverage Association, a lobbying group, trumpeted the “smaller package sizes” on offer at grocery stores. This fight for smaller bottles was perhaps most famously encapsulated by Michael Bloomberg's 2013 war on soda and the banning of “Big Gulp” style beverage offerings.

But while this might benefit American waistlines and dental health today, it could be contributing to the affects of climate change both now and in the future, the study reveals.

What’s new — The new study looked at the efficiency of different PET bottles. Basically, efficiency here refers to the “quantity of consumable product delivered relative to the mass of plastic package used to contain it.”

In other words, how much fizzy drink is available, compared to the plastic packaging needed to contain it?

According to the study, the least efficient bottles are also the smallest. Defined in the study as bottles under 16 ounces (a-okay as far as Bloomberg was concerned), these smaller bottles were “clearly less efficient,” the study says, compared to midsize or large bottles.

Rafael Becerril Arreola, an assistant professor of Marketing and lead author of the study, tells Inverse he wasn’t surprised by the findings. What makes small bottles so bad, he says, is to do with their design.

“Every bottle needs a certain amount of plastic for the neck and lid, and that amount is somewhat constant regardless of the size of the bottle,” he explains.

The neck of a plastic bottle doesn’t typically contain any of the beverage itself, and, thus, “takes a larger percentage of the weight in smaller bottles than in larger bottles,” he says.

Instead, medium-sized bottles — defined in the study as anything between 16 to 100 ounces — get the gold medal in terms of overall efficiency.

Digging into the details — Becerril and his co-authors used PET bottle sales in Minnesota from 2009 through 2013 in their study, which they say is a good analogue for the national picture of consumption and recycling.

To better understand bottle efficiency in Minnesota, Arreola and his team used four different metrics of measurement. They were:

• The determinants of bottle weight
• The relationship between bottle capacity and bottle weight
• The relationship between bottle capacity and PET waste
• The potential benefits of shifting the capacity of bottles used

Two things they did not consider, Becerril tells Inverse, were “secondary” and “tertiary” packaging. PET bottles don’t exist in a vacuum, after all: they come with brand labels, bottle caps, are shipped on wooden pallets, and are often protected by yet more plastic wrapping.

The study’s focus was solely on the bottles themselves, but future work might try to take these other points into account to fully understand how these drinks bottles add up to waste.

Why it matters — The study poses an important question for public-health officials and consumers to consider: What if a mere 20 percent of smaller bottle sales were instead shifted to medium-sized bottles?

This hypothetical showed a reduction of PET used “by over 1 percent in each year in the sample.” Zooming out to the entire United States, that 1 percent shows a potential reduction of 9,052 tonnes in PET waste every year.

What’s next — To encourage people to switch over to medium-sized bottles, the study offers a few suggestions. Soda taxes have had some effect on purchasing habits, and the study says that “consumption taxes on large, single-use containers” could further push consumers towards mid-size options — but this still runs the risk of pushing them toward the smallest bottles. Better would be to remove them entirely from consumers' paths. More research is needed to understand how this plays into the need for public-health measures geared around reducing soda consumption. For now, we suggest you get a reusable water bottle and just refill it when you need more juice.

Perhaps if “bottle efficiency was reported on the label,” like calories and sugar are, then consumers might look at each bottle differently, this study's authors suggest.

Abstract: Plastic pollution is a pressing issue because authorities struggle to contain and process the enormous amount of waste produced. We study the potential for reducing plastic waste by examining the efficiency with which different polyethylene terephthalate (PET) bottles deliver beverages. We find that 80% of the variation in bottle weight is explained by bottle capacity, 16% by product category, and 1% by brand. Bottle weight is quadratic and convex function of capacity, which implies that medium capacity bottles are most efficient at delivering consumable product. Local data on PET bottle sales and municipal waste recovery validate the findings. A 20% shift in consumption from smaller to larger bottles could reduce the production of PET waste by over 10,000 t annually in the U.S. alone.