You'd never buy a Barbie without knowing she's made of plastic. It's printed right there on the box, and nobody's surprised by it. So here's a stranger question: do you know what your leggings are made of?
Everyone knows Barbie's plastic. Did you know a lot of your "soft" fabric is too?
Most activewear on the market is nylon or polyester — both are plastics, just spun into thread instead of molded into a doll. The label tells you exactly how much: fabric composition is listed as a percentage on every garment, and it's the one honest indicator of how much synthetic, petroleum-based material is sitting against your skin. Not how something feels off the rack. What it's actually made of.
Why checking the label actually matters
Your skin doesn't just sit against fabric — it absorbs from it, and heat and sweat change how much. Research from the University of Birmingham (April 2024) found the first experimental evidence that chemical additives used in plastics, including flame retardants, can leach out of synthetic material and into sweat, where more hydrated skin absorbs significantly more than dry skin. That's exactly the condition you're in during a workout: warm, sweaty, and in prolonged contact with the fabric.
This isn't a reason to panic about every synthetic garment you own. It's a reason to actually read the label before you buy your next set of leggings, rather than going on how the fabric feels in the shop.
What is nylon?
A plastic made from petroleum-derived chemicals. Look for "nylon" or "polyamide" on the label — the higher the percentage, the more synthetic the garment.
What is polyester?
It's PET — the exact same plastic used in water bottles — melted down and spun into thread. It's cheap and durable, but it doesn't biodegrade, and washing it sheds microplastic fibres into waterways with every load.
My rules when buying natural activewear
I don't chase 100% natural fibres for everything — some synthetic content is genuinely doing a job (stretch, structure, moisture-wicking). But I do set a ceiling:
- Activewear: 10% or less synthetic — usually just what's needed for stretch and structure.
- Underwear: 5% or less synthetic, since it sits against more delicate skin for longer and needs less stretch to begin with.
Barbie doesn't sweat in hers. You do.
That's exactly why I built an activewear collection that's 90% GOTS-certified organic cotton. GOTS (Global Organic Textile Standard) is a globally recognised certification that covers the entire supply chain — the fibre is grown organically and processed without chlorine bleach, formaldehyde, or toxic azo dyes, audited at every stage from farm to finished garment.
Leggings, shorts, crop tops, tanks — every piece hand-designed and made with a fabric composition you can actually check.
Shop the organic activewear collection — shop now →
Curious what's actually inside most gym leggings? Read What's Actually in Your Activewear? for the full nylon vs. polyester breakdown.
Sources: University of Birmingham research on plastic additives leaching into sweat (2024); Global Organic Textile Standard (GOTS) certification criteria.