What a sports bra taught us about polyester

In 2022, the Center for Environmental Health sent sports bras and athletic shirts to EPA-certified labs and got back a result that reframed a whole aisle of the store. The polyester-spandex garments could expose wearers to up to 22 times California's safe dermal limit for BPA. Some individual readings came back at 40 times. Legal notices went out to 19 major activewear brands, which tells you this wasn't one rogue factory.

BPA is a plastics chemical most of us learned to avoid in water bottles a decade ago. Finding it pressed against the skin of a garment designed for sweating is a legitimately unwelcome discovery, and it's fine to say so plainly.

But the same testing carried a second finding that's easy to miss and far more useful. BPA turned up only in polyester-spandex blends. Pure cotton, wool and linen garments in the testing showed none. Not lower levels. None.

That turns the fibre-content line on a tag from trivia into a filter. You can't see BPA, smell it, or wash it out of a synthetic blend where it's part of the material itself. What you can do is read two words, "polyester" and "spandex," and know which category of risk you're holding. For the workouts where you want a simpler answer, cotton and wool are sitting right there.

One honest caveat: this filter only works if the label tells the truth, and a Dutch government-commissioned study of over 10,000 garments found 41% of fibre labels inaccurate. Independent verification of what a garment is actually made of, the kind Lynen surfaces when you scan, closes that gap.

The sports bra story isn't really about bras. It's proof that fibre choice, the one variable printed on every tag, does measurable chemical work. Use it.