Reference
The smallest number on the label sets the rules
A garment marked 95% cotton and 5% elastane is not a cotton garment, at least not for the purposes of washing it. It is an elastane garment, and everything you may safely do to it is decided by that 5%.
Last updated 26 July 2026
This is the label that is actually required
There is a small inversion worth knowing before anything else.
In the European Union, care instructions are not legally required. The symbols come from EN ISO 3758, a voluntary standard, and a manufacturer who prints none at all has broken no rule. But fibre composition is mandatory, under Regulation (EU) No 1007/2011.
So the tag everyone obeys is optional, and the tag everyone ignores is the binding one. Given that a care instruction only ever certifies one method anyway, the composition is often the more informative of the two.
How the numbers work
Fibres are listed with their percentage by weight, in descending order. The first name is always the largest share, and the list is a ranking.
By weight matters. A dense fibre can be a small part of what you see and a large part of the number, and a bulky one the reverse — the percentage is not telling you what the fabric looks or feels like.
Two other conventions worth recognising. Fibres not covered by the regulation's own list may be described simply as "other fibres" with a total percentage — that is a legal category rather than evasiveness. And percentages carry a manufacturing tolerance, which is where it gets more interesting than expected.
“100% cotton” does not mean the same thing everywhere
| EU | US | |
|---|---|---|
| Tolerance on a blend | ±3% | ±3% |
| Tolerance on a “100%” claim | Applies | None |
| Undeclared other fibres | Up to 2% (5% if carded), where technically unavoidable | Not permitted under a 100% claim |
| Ornamentation | — | Up to 5% excludable, if stated |
In the EU, a small quantity of undeclared other fibre is lawful where it is technically unavoidable in good manufacturing practice — up to 2% of total weight, or 5% for carded products. In the US, a claim that a product is composed wholly of one fibre gets no tolerance at all, though up to 5% of decorative fibre can be excluded if the label says so.
None of that makes labels untrustworthy. A tolerance is an allowance for the realities of manufacturing, not a licence to misdescribe. But it does mean the same three characters carry different legal weight depending on which market the garment was sold into — the second place on this site where a US and a European label say the same thing and mean something different.
Vulnerabilities concentrate. Virtues dilute.
Now the part that matters.
A blend can only be treated as gently as its most fragile component demands. Five percent elastane still fails at tumble-dryer temperature, and when it does, the garment loses its shape — the other 95% cannot compensate for it. The weakness does not get diluted by being outnumbered.
Strengths behave in the opposite way. Five percent wool in a polyester shirt does not make the shirt odour-resistant, and a little linen in a cotton blend will not make it stronger when wet. Benefits are proportional. Vulnerabilities are not.
| If you see | Typically | It imposes on the whole garment |
|---|---|---|
| Elastane, spandex, Lycra | 2–5% | No dryer, no hot wash, no fabric softener. Heat damage accumulates and does not reverse |
| Wool | any | No biological detergent, minimal agitation, no heat |
| Silk | any | pH-neutral detergent only, no enzymes, keep it out of sunlight |
| Viscose, rayon | any | Loses roughly half its strength wet — never wring |
| Acetate | any | Weak when wet, and damaged by several common solvents |
| Linen | usually the majority | Nothing — it is one of the few fibres that is stronger wet |
Which is why the practical instruction is: read the list backwards. The last fibre named is the smallest, and it is usually the one that will decide what you are allowed to do.
When two fibres want opposite things
Blends regularly contain fibres with incompatible requirements, and the care label has to pick a side. It always picks the same way.
- Wool and polyester. Wool wants cool and gentle. Polyester wants heat, because its problem is trapped skin oil and oil needs heat to shift. The label sides with wool — felting is irreversible, residual oil is not.
- Cotton and elastane. Cotton is happy at 60 °C. Elastane is not. The label sides with elastane.
- Cotton and wool. Cotton is fine with ordinary alkaline detergent, which damages wool keratin. The label sides with wool.
The rule underneath: the care label always sides with the most fragile fibre in the mix. So when a blend specifies a lower temperature than you would expect for its majority fibre, that is not manufacturer over-caution. It is arithmetic, and following it is correct.
What a recycled claim actually certifies
Composition labels increasingly sit alongside a recycled-content claim, and two of the common marks mean very different things while looking equally green.
| RCS | GRS | |
|---|---|---|
| Minimum to be certified | 5% | 20% |
| Minimum to label the product | 5% | 50% |
| Covers processing, chemicals, social criteria | No | Yes |
The Recycled Claim Standard verifies recycled content and chain of custody, and nothing else — a product can carry it with 5% recycled material and no environmental or social requirements at all. The Global Recycled Standard requires at least 50% before the logo may go on a product, and adds requirements covering processing, chemical restrictions and social responsibility. Between 20% and 50% a product can be GRS-certified but may not display the mark.
So a hangtag saying "recycled" without naming a standard and a percentage has told you approximately nothing.
And there is a limit to what any of these marks address. Chain-of-custody certification is about the fibre. It says nothing about the energy used to make the garment, the packaging, the shipping, or how long the thing will last — and durability is the variable this whole site is about. A garment washed correctly for ten years is doing more than one made of recycled polyester and destroyed in eighteen months by a tumble dryer.
The short version
- Composition is legally required in the EU. Care instructions are not.
- Fibres are listed by weight, largest first. Read the list backwards.
- “100%” allows a little slack in the EU and none in the US.
- The smallest fibre usually sets the rules. 5% elastane governs the garment.
- Vulnerabilities concentrate; virtues dilute.
- Blends side with the fragile fibre. That is why the temperature looks low.
- RCS can mean 5% recycled. GRS on-product means 50%.
The habit worth building is small: when you buy something, read the composition before the care symbols. The symbols tell you what one manufacturer decided to certify. The composition tells you what the garment actually is, and from that you can usually work out the rest yourself — which was the point of learning the symbol grammar in the first place.