Fibres
Are biodegradable synthetics microplastic free?
Recycled synthetics use less new fossil feedstock. They shed the same microfibres as any other polyester.
Last checked July 2026.
Two words get used as if they mean the same thing, and they do not. Bio-based tells you where the carbon in the fibre came from, often sugarcane or corn rather than oil. Biodegradable tells you what happens to that fibre once it leaves your washing machine. A bio-based fibre can sit in a river for just as long as a fossil-derived one.
The axis that matters is persistence
When I look at a synthetic I am asking one question: how long does what it sheds stick around. Conventional and bio-based elastane sit near the top of that scale. Biodegradable elastane sits meaningfully lower, but nowhere near a natural fibre, which barely registers. That is a real difference and it is a difference of degree, not of kind.
What the test certificates actually prove
Most biodegradability claims rest on a controlled composting test such as ISO 14855-1. That measures breakdown in warm, wet, microbially rich compost over a set period. It is a laboratory condition. It is not a cold river, a sewage works, or the open sea, and it is not a claim about what your washing machine sends down the drain. A certificate is evidence about test compost and chemistry, and it should be read that way.
Where this leaves a garment
What a pair of leggings with biodegradable elastane sheds is designed to break down faster than what the conventional kind sheds. It is still an engineered synthetic, so it does not become a natural fibre and it does not earn a place in my verified tiers on that basis. If the rest of the composition does not stand up, the elastane does not rescue it.
The two mistakes I see most
The first is treating bio-based as if it meant biodegradable. The second is treating biodegradable as if it meant microplastic free. Neither follows, and both appear on otherwise careful product pages.
Where this comes from
- ISO 14855-1, determination of ultimate aerobic biodegradability under controlled composting conditions
- Napper and Thompson 2016, release of synthetic microplastic fibres from domestic washing of polyester, acrylic and polyester-cotton textiles, Marine Pollution Bulletin
- Cradle to Cradle Certified product standard, material health and circularity criteria
I check labels like this one product at a time. If you want me to do it while you shop, the Chrome extension reads the page you are on and tells you what is actually in it.