You can pour a soda, finish it, and drop the bottle in the recycling. That bottle is made of a plastic called PET. Your favorite workout top is very likely made of the same thing. Polyester is plastic. The two start in nearly the same place.
We don't think of it that way, because polyester feels like fabric. It's soft, it's cheap, it holds color, it shrugs off wrinkles. But under a microscope it's a petroleum product, spun into threads thin enough to weave into a shirt. About 60 percent of all the clothing made today is polyester, and almost all of it comes straight from fossil fuels, according to the Textile Exchange, which tracks what the world's clothes are made of. More of it is spun every year.
Your gym top and a soda bottle start in nearly the same place.
So what does it mean to wear plastic all day? A few things, and they're worth knowing.
It doesn't breathe
Cotton and linen drink up water. Polyester pushes it away. That is the reason it dries so fast, and also why a polyester shirt turns into a little greenhouse against your skin. Heat and sweat have nowhere to go. That is the clammy feeling at hour three of a synthetic dress, and the reason gym clothes hold onto a smell that a cotton tee never does. Bacteria love warm, damp plastic.
Warmth and damp do something else, too. They loosen the chemistry sitting on the fiber and pull it toward your skin. We wrote about those studies here: a sweaty polyester shirt is a more active thing than a dry one.
It sheds
Every time you wash polyester, it breaks off tiny plastic threads too small to see. One ordinary load can release close to half a million of them, according to researchers at the University of Plymouth who sat down and counted. Those microfibers slip through the washing machine, past the water treatment plant, and out into rivers and oceans. They also drift in the air of your home. We are still learning what a lifetime of breathing and swallowing tiny plastic does to a body. The honest answer is that nobody fully knows yet, which is its own kind of warning.
It carries things
Plastic is a good messenger for other chemicals. The dyes that give polyester such bright color, the finishes that make it stretch or resist wrinkles, the leftovers from making the plastic in the first place: they all ride along in the fiber. Some of them are the hormone-copying chemicals that keep turning up in clothing tests. The plastic is not only the problem. It is also the delivery truck.
What to do about it
None of this means polyester is evil, or that you should empty your closet tonight. It means a few small choices are worth making with your eyes open.
For the clothes that live against your skin the longest, the ones you sleep in, work out in, and wear all day, reach for fibers that started as a plant or an animal instead of oil. Cotton, linen, wool, hemp, silk. Your body can tell the difference, even when your eyes can't.
Wash your synthetics less often and in cooler water. A microfiber-catching laundry bag helps too, and keeps a little more of the plastic where it belongs.
And turn the tag over. The composition label, the one that reads 100% polyester or 95% poly 5% elastane, is the ingredient list nobody taught you to read. Once you start seeing it, you can't stop. That is the point.
Polyester isn't going anywhere; it's most of what hangs on the racks. But the more of us who know what it is, the more the racks will have to change. Knowing what you're wearing is where it starts.