It's not just you – bottles and cartons are now harder to open. We found out why.

It's not your imagination: Beverage containers for milk, soda and water have gotten harder to open in recent years because their plastic screw top caps have been shortened to save plastic.

It's a subtle shift in products opened by millions of Americans every day – a change the industry touts as saving not just plastic but also weight, both of which lead to less energy to transport them, a lower carbon footprint and a lower cost to produce the packaging.

"That’s one of the reasons that people transitioned from glass and metals, because plastic is so much lighter and weight is such a large percentage of contribution toward your carbon footprint," said Patrick Krieger, vice president of sustainability at the Plastics Industry Association.

But it's also why caps on half-gallon paper cartons of milk and juice and plastic soda and water bottles are harder to turn and why the body of plastic bottles sometimes twist along with the cap when you try to open them.

The old-style milk carton caps were 21 millimeters tall, while the new ones are 17 millimeters ‒ a difference of about 19% that makes them harder to grip, said Min DeGruson, a professor and director of packaging at the University of Wisconsin-Stout.

Four millimeters – about an eighth of an inch − might not seem like a lot, but it matters when you're trying to open something, said Alaster Yoxall, a professor of packaging ergonomics at Sheffield Hallam University in the United Kingdom.

“The shorter the height, the less grippable area," he said. "So we can't apply our maximum grip force, and we struggle."

Wrap rage

Consumers have noticed.

"We keep a pair of pliers in the utility drawer in the kitchen to open them now," said Fred Wolden, a retired marine contracting officer with the U.S. Coast Guard who lives in Center City, Wisconsin.

It's not that they're impossible to open by hand, but it's just a little more aggravating. "You used to have three or four threads to turn. Now you only have two, so it's harder," he said. "You can't really get your hand on it."

For Jack Whalen, a retired sociologist in Pioneertown, California, it's a nuisance.

"I have indeed noticed how the screw caps have gotten shorter," he said. The newer, shorter caps "are a little more likely to slip out of my hand."

He's right. Yoxall has researched it, and the difficulty boils down to this formula: T= μ*N*r, where μ is the Greek symbol for the coefficient of friction, N is the grip force and r is the radius of the lid.

In Britain there's even a term for packages that are harder and more frustrating to open: "wrap rage."

"The packaging industry is being hammered to reduce its environmental impact, that's the thing everybody's focusing on," Yoxall said. "But people like me, we're knocking on the door and gently saying 'Yeah, but people have to use this stuff – they have to be able to get into it."

The changes happen slowly and at different times in different places, Krieger said, so they're not always easy to spot.

"You need to build new equipment," he said. "It is a very gradual process, and that’s why it’s very hard for us to notice as consumers that these things are happening. It seems that things are all of the sudden different when it’s it’s actually been going on for a long time."

Anytime you adjust packaging, you have challenges, said Ben Yee, director of processor partnerships with the California Milk Advisory Board.

"Retailers have seen customer complaints about the shorter cap being hard to open and close," he said.

Why did milk carton plastic caps get shorter?

Plastic spouts for cardboard milk and juice cartons were first introduced in 1990. The Spout-Pak was a product of International Paper, which made milk cartons, a market that was steadily eroding as consumer switched to plastic milk jugs.

Consumers liked the convenience of the new spouts, which were less likely to spill or leak. They also allowed customers to safely shake the contents without accidents. Milk producers liked them because the provided an airtight, tamper-resistant seal that helped keep milk, juice and other liquids fresh longer.

About 17% of U.S. milk was sold in paper cartons in 2023, compared with 82% sold in plastic jugs, according to the U.S. Department of Agriculture.

The shift to the new, shorter caps is mostly to reduce weight, which reduces shipping costs and therefore saves money, said Rafael Auras, who chairs Michigan State University's program in packaging sustainability.

"For several decades, there has been a strong incentive to reduce the weight of containers. From 2005 to 2010, Walmart mandated that all their suppliers reduce their packaging weight," he said.

The milk industry has followed suit. The change also has coincided with efforts over the past decade or so to reduce plastic packaging more broadly.

"This was largely driven by the processors and packaging companies as pressures increased to reduce waste, reduce cost and be more sustainable," Yee said.

The same cap shortening has happened in soda and water

The plastic lids for plastic soda pop and water bottles got smaller first.

A study by the Oregon Department of Environmental Quality found that a typical water bottle weighed 13.3 grams, but shrinking the cap and thinning the plastic bottle reduced the global warming footprint of the package by about 18%.

In some cases, things went further than consumers were comfortable with.

"People want to use less plastic and still get the job done," Krieger said. "We’ve all bought that water bottle that seems very flimsy and crinkly."

At a certain point consumers start complaining "I can’t open it" or "It’s too flimsy," he said.

That's when light weighting becomes "right weighting," he said. "We're ensuring that we hit the happy middle ground of making sure it's as thin as possible but making sure you can still open it."

Next up: Tethered caps

The next likely disruption for your favorite beverage container will come in the form of what are known as "tethered caps." As the name suggests, these are tied to the bottle with a small bit of plastic so the cap doesn't come off even when the bottle is open.

By keeping the cap attached to the plastic spout assembly, the cap can't get lost and contribute to plastic waste and especially ocean waste, Degruson said.

The new caps haven't appeared in the U.S. yet but became required by European Union law in July, she said.

They've already gotten pushback there.

"Those tethered caps get a lot of complaints because when you have the cap tethered, it gets in the way" of drinking and sometimes pouring, she said. "It might not be that the current design is the best."

The caps probably will come to the United States eventually, she said, but for now there's no regulation requiring them.

In the end, Wolden, the retired marine contracts officer, isn't convinced such changes are about saving the planet.

"I think it's baloney," he said. "There's no thought about the customer here. It's all about the dollar."

This article originally appeared on USA TODAY: Shrinking plastic caps make bottles and cartons harder to open