Before you toss another empty plastic bottle into the recycling bin in your kitchen, you might want to make sure the cap is still attached. As Lifehacker points out, when you remove the cap from a plastic bottle, “you’ve essentially thrown it right in the garbage.”
This advice seems to go against everything we’ve been taught in the past. It’s true that bottles and caps are typically made of different kinds of plastic—and that used to pose problems at recycling plants. “In the past the plastics recycling industry was not able to effectively recycle bottles with caps on so the message to remove the cap was created,” the Association of Plastic Recyclers explains on its website [PDF].
Recycling technologies have improved since then, and keeping the lid on is no longer an issue. Essentially, the two components are separated naturally in a process referred to as a water bath. The bottles float and the caps sink, making it easy to separate the two materials.
On the other hand, removing the caps can cause them to be improperly sorted early on in the recycling process. Because of their small size, individual caps are often sorted into piles of landfill-bound waste. They are also common ocean pollutants, and can seriously harm marine life if they are ingested. By some estimates, 5 billion plastic caps pollute the environment in California alone each year.
It’s also common for people to crush plastic bottles before placing them in the bin, but that should also be avoided. That’s because they could be confused for paper during the sorting process and end up in the wrong place (at least that's the case if your community uses a single-stream recycling program, in which everything set to be recycled ends up in the same bin). “Retaining a 3D form can help containers be successfully sorted,” according to The Association of Plastic Recyclers.
In summary: Dump out any liquids left inside the bottle, replace the cap, and toss it in the recycling bin—but be sure to check with your individual recycling program to see if there are any exceptions to the rule.
A version of this story ran in 2019; it has been updated for 2023.