TL;DR — Cotton on its own is a great fibre — breathable, soft, takes dye beautifully, biodegrades at the end. But the "cotton-everywhere" reputation has gotten ahead of the reality. Especially in jeans. A pure-cotton jean used to be standard. Most pairs now are something like 98% cotton, 2% elastane, sometimes with polyester thrown in. That bit of stretch feels nice, but it means the jeans can't be recycled, they'll sag at the knees long before pure denim would, and they shed microplastics every wash. The label tells you which one you're holding.

Try this little experiment. Walk over to your wardrobe, pull out the three pairs of jeans you wear most, and check the composition tag on the inside of each one. I'll wait.

If you find a pair that says "100% cotton," congratulations — that's increasingly rare. Most of you will be looking at something like "98% cotton, 2% elastane," or maybe "92% cotton, 6% polyester, 2% elastane." That's the modern jean. And it's a very different garment from what your parents called denim.

Cotton, On Its Own, Is Great

Let me say this first because it matters. Pure cotton is a brilliant fibre. It's breathable, it's soft against your skin, it absorbs moisture, it takes dye gorgeously (which is why indigo and cotton became the iconic denim pairing in the first place), and at the end of its life it biodegrades cleanly back into the soil.

For everyday clothes against your skin — T-shirts, underwear, jeans, jumpers — cotton is genuinely lovely. Green light. The traffic-light grade isn't the issue here. The issue is that "cotton" on the label has quietly stopped meaning what it used to mean.

The Stretch Problem

Sometime in the mid-2000s, denim brands figured out that adding a few percent of elastane (also known as spandex or Lycra) made jeans feel dramatically nicer to wear. You can squat in them. You can sit down without the waistband digging in. Skinny jeans wouldn't really exist without it.

Customers loved it. Brands loved it because the comfort masked some other corner-cutting (cheaper cotton, looser weaves). And now you basically can't find non-stretch jeans on most high streets. The default has shifted from "100% cotton, comfortable enough" to "98% cotton, 2% elastane, comfortable like leggings."

Then a few brands started adding polyester too — three or four percent for "shape retention" — and now a not-insignificant chunk of the denim market is genuinely a multi-fibre blend masquerading as the most natural-sounding garment in your wardrobe.

The most natural-sounding garment in your wardrobe has quietly become a blend. And once you see it on the label, you can't unsee it.

Why the Stretch Costs You

Here's the trade-off nobody mentions on the price tag.

That little bit of elastane has three big consequences, and none of them get advertised:

  • The jeans can't be recycled. Mechanical denim recycling needs a near-pure cotton stream. Even 2% elastane contaminates the whole garment for that process. We've got a whole separate piece on why this is such a mess.
  • They sag faster. Elastane fibres lose their bounce after enough wear cycles, and the knees, seat and waistband all go baggy long before a pure-cotton jean would have given up.
  • They shed microplastics. Every wash releases small amounts of elastane (and polyester, if it's in there) into the water system. Pure cotton doesn't do this.

And if there's polyester in the mix, those issues are even worse. A 92/6/2 cotton-poly-elastane jean is much closer to a synthetic garment than a natural one, even though "cotton" is still the headline.

The Label Test

You don't need to give up jeans. You just need to read what you're buying.

The rule of thumb I use: anything 95% cotton or above with only elastane in the rest is a reasonable compromise — comfortable, mostly natural, still flawed but understandable. Anything below 95% cotton, or anything with polyester or recycled polyester in the mix, is genuinely closer to a synthetic garment, and you should price it as such.

And if you can find genuinely 100% cotton denim — usually from heritage brands, raw denim labels, or some of the better workwear lines — buy it. It'll be stiff for the first few weeks. It'll fit perfectly to your body after about three months. It'll last for a decade. And when its life is finally over, it can be recycled or composted in a way no stretch jean can.

The Traffic-Light Verdict

Pure cotton is a strong green light. The cotton blends quietly taking over denim are an amber at best — and a red if there's polyester in the mix.

The honest line: 100% cotton is one thing. A cotton blend is a very different garment, even when the cotton is the headline. Most people have no idea which one they're holding, because most people don't flip the label. Once you start, you can't stop.

Flip Every Label Without Flipping Every Label

Fibr is a free Chrome extension that shows you the fabric composition of every garment — right on the product image — while you browse Zara, H&M, Mango and the rest. So when a pair of "cotton" jeans turns out to be 92% cotton, 6% polyester, 2% elastane, you'll see it before you click. Buy on purpose.