What your clothes are actually made of: viscose, lyocell and the fibres you shed

A garment’s composition label is a specification, and almost nobody reads it. Cotton, viscose, lyocell, polyester and acrylic can be cut into the same dress and hang almost identically on a rail. They do not age the same, wash the same, breathe the same, or come from the same kind of factory — and those differences are not marketing copy. They are chemistry, and the chemistry has a history.

Start with cellulose, because most of the confusion lives there. Cotton is cellulose grown as a fibre. Viscose, modal and lyocell are cellulose too — usually from wood pulp — but dissolved and spun back into filament, which is why they are called regenerated fibres and why they can be made to feel like silk. The three share a raw material and differ in exactly one thing: the solvent used to dissolve the pulp. That one thing turns out to decide almost everything about their environmental and human cost.

Viscose is the old process, in commercial use since the early twentieth century, and its solvent is carbon disulphide. The occupational medicine literature on it is not ambiguous. A five-year follow-up of viscose rayon workers in Britain found fourteen deaths from coronary heart disease in the exposed group against three among controls, with nearly a quarter of exposed men reporting angina against thirteen percent of controls. A separate morbidity study found ischaemic heart disease, nephritis and hypertensive disease all significantly more prevalent among spinners and cutters with ten or more years of exposure, with prevalence ratios of 2.3 for ischaemic heart disease and 7.6 for kidney disease. Carbon disulphide is also an established neurotoxicant. Modern plants in well-regulated countries capture most of it; the industry’s history, and the reason a great deal of viscose is now made where regulation is thinner, is that many plants did not.

Lyocell is the same cellulose with a different solvent. Courtaulds developed the process in 1988 using N-methylmorpholine N-oxide — NMMO — which is low in toxicity and, crucially, recoverable. In Lenzing’s TENCEL process the solvent and water are separated by evaporation and distillation and fed back into the loop; the company reports more than 99.8% of the NMMO recaptured. The fibre that comes out has the drape and cool hand of viscose, with a wet strength viscose lacks — lyocell does not go limp and fragile in the wash the way viscose can. When two labels read “viscose” and “lyocell”, that is the difference you are choosing between: an open chemical loop or a closed one, in a fibre that feels the same in the hand.

Synthetics carry a different debt, paid after purchase rather than before. Polyester is the most-used fibre on earth and, as a fibre, it is excellent — strong, cheap, quick-drying, colourfast. Its cost is the shedding. Napper and Thompson’s 2016 study in Marine Pollution Bulletin washed polyester, polyester-cotton and acrylic garments at 30 and 40 degrees with various detergents and conditioners and counted the fibres in the effluent. A single 6 kg load of synthetic clothing released between 140,000 and 700,000 fibres. Acrylic shed the most — about 122 microfibres per gram of fabric — against roughly 83 for polyester and 23 for the polyester-cotton blend. Those fibres are too small for most treatment plants to catch, and they are why microplastic surveys of shorelines and deep-sea sediment keep finding textile fibre. Every wash of a synthetic garment is a small, measurable emission, and the fibre on the label decides how large.

Composition also predicts how a garment ages, which is what most people are actually asking when they ask whether something is “good quality”. Cotton softens and fades; it wears out at the friction points but rarely fails suddenly. Viscose loses strength when wet and can shrink or distort in a machine, which is why so many viscose dresses come out of the first wash a size smaller and a shade duller. Polyester keeps its shape and colour almost indefinitely and pills where it rubs, because the fibre is strong enough that a broken end stays attached and balls up rather than shedding. Wool felts if agitated warm. None of this is folklore; each behaviour follows from the fibre’s structure, and each is on the label before the garment is bought.

Blends complicate the reading, and they are most of what is sold. A 95/5 cotton-elastane jersey is essentially cotton with stretch; a 50/50 poly-cotton is a different fabric from either parent, cooler than polyester and more stable than cotton, and Napper and Thompson’s figures show it sheds far less than pure polyester. The rule for blends is to read the majority fibre for feel and care, and the minority fibre for what will fail first — elastane goes before cotton, and when it goes the garment is finished however sound the rest of it is.

None of this makes any fibre forbidden, and the pieces that pretend otherwise are not being honest. A polyester rain shell earns its place by doing something cotton cannot do. Elastane is why trousers fit. Acrylic is warm and cheap and, for a garment worn a few times a year and rarely washed, sheds very little in practice. The point is that the choice is informed or it is not, and the information is printed on a tag sewn into the side seam, where nobody looks.

It is also why ZIMRICS records composition as a structured field on every garment rather than a free-text note. Once fibre is data, the wardrobe can answer questions no rail can: which of my things shed in the wash; what here is regenerated cellulose and from which process; which garments should never see a hot cycle. The care instructions on the same label become rules the app can apply, instead of pictograms nobody has memorised. And when the European Union’s digital product passports arrive for textiles later this decade, composition will be one of the first fields they carry — so a wardrobe that already stores it is a wardrobe ready to read them.

A practical rule, for what it is worth. Prefer natural or closed-loop cellulose — cotton, linen, lyocell — next to the skin, where breathability matters and washing is frequent. Accept synthetics where their performance is the reason you bought the garment, and wash them as rarely as decency allows, in a full load, cold. Treat acrylic as an occasional fibre. And before buying anything described as “silky”, turn the label over and see which cellulose it is. The fabric will feel the same either way. The factory did not.