Synthetic Fibers · Petrochemicals
Fast fashion's backbone — and the ocean's problem
It's in 52% of all clothing sold today. It's derived from crude oil. And every time you wash it, it sheds invisible plastic into the water supply. Here's what's actually in that $25 bedsheet.
Polyester — specifically PET (polyethylene terephthalate) — is a synthetic polymer made from two petroleum-derived monomers: ethylene glycol and terephthalic acid. They're joined by ester linkages (–COO–) in a condensation reaction, releasing water as a byproduct and building chains that can reach 50,000–150,000 daltons in molecular weight.
The result is a highly regular, largely non-polar chain with aromatic (benzene) rings at regular intervals. This molecular regularity is what gives polyester its remarkable properties — and its most frustrating ones.
You've experienced this. A polyester athletic shirt that smells fine when dry, but the moment you start sweating it reeks — even if you washed it yesterday. This is not a hygiene failure. It's molecular chemistry.
The odour compounds in sweat — primarily isovaleric acid, butyric acid, and various sulfur compounds — are small, non-polar molecules. The PET chain, also largely non-polar, has a chemical affinity for them. These compounds absorb into the amorphous regions of the polyester fiber and bond via van der Waals forces. Water-based washing barely touches them — the detergent can't out-compete the fiber-odour affinity.
Cotton absorbs sweat into the fiber matrix, then releases it during washing as the hydrogen bond network dissolves. Polyester traps odour compounds and holds them.
When polyester fabric is agitated in a washing machine, mechanical friction breaks individual filaments at their weakest points — crystalline boundary zones — releasing fiber fragments typically 1–5 micrometres in diameter and under 1mm in length. These are microplastics.
They're too small for conventional wastewater treatment to capture. They pass through treatment plants into waterways, where they accumulate in sediment, are ingested by marine organisms, and travel up the food chain. They've been found in deep ocean sediment, Arctic sea ice, human placentas, lung tissue, and blood.
This is not a future risk. It is a present, documented, unresolved contamination.
PET is one of the most chemically stable polymers ever synthesised. At room temperature, in soil or water, it resists biological and chemical degradation almost completely. Estimates for full environmental breakdown range from 20 to 500 years depending on UV exposure and conditions — most modeling puts it at 200+ years in landfill or ocean.
Unlike natural fibers — which biodegrade into carbon dioxide, water, and organic matter — polyester fragments into progressively smaller microplastics rather than breaking down chemically. The polymer chain remains. It just gets distributed more widely.
| Material | Landfill breakdown | Ocean breakdown | End product |
|---|---|---|---|
| Cotton | 1–5 months | Weeks–months | CO₂, H₂O, organic matter |
| Wool | 1–5 years | Months–years | CO₂, H₂O, nitrogen |
| Linen | 2 weeks–3 months | Days–weeks | CO₂, H₂O, organic matter |
| Silk | 1–4 years | Months | CO₂, H₂O, nitrogen |
| Nylon | 30–40 years | Unknown, very slow | Microplastics |
| Polyester (PET) | 200–500 years | 200–500 years | Progressively smaller microplastics |
| rPET (recycled) | 200–500 years | 200–500 years | Microplastics (same as virgin PET) |
Polyester's dominance isn't accidental. It's the result of economics, supply chain efficiency, and a deliberate industry pivot in the 1990s and 2000s. The fiber is cheap to produce, stable to ship and store, accepts dye easily, resists shrinking and wrinkling in transit, and can be engineered for specific performance characteristics. For an industry optimizing for cost and volume, it's a nearly perfect material.
What the economics didn't price in was end-of-life, microplastic emission, or petrochemical dependence. Those costs were externalised — onto ecosystems, waterways, and ultimately consumers and governments.
Minimising microplastic shedding and maximising the fiber's lifespan reduces harm at both ends. The chemistry dictates some non-obvious rules.
The answer isn't "never use polyester." It's using the right material for the application. For sheets, underwear, and anything worn close to skin for extended periods — polyester is the wrong choice. For specific technical applications, it has genuine advantages.