How can I tell what fabric something is made of?

This comes up more often than you would think — a label washed off, a charity shop find, an inherited garment, a length of fabric with no selvedge marking. You do not need to identify the exact fibre. You need to know which of three families it belongs to, because the family decides the wash.

Safety

What you'll need

• a single thread pulled from a seam allowance
• tweezers or long-nosed pliers
• a lighter or a match
• a sink, or a ceramic dish
• a glass of water

Step by step

1. Start with feel, weight and drape.Cotton feels cool and soft with moderate drape. Linen is crisp and slightly irregular with visible slubs. Wool is warm and springy and recovers when squeezed. Silk is cool, smooth and light, with a faint rustle. Polyester feels slick and slightly plasticky. Viscose feels cool and fluid, like silk but heavier and more limp.
2. Do the water drop test.Put a drop of water on a hidden area. It soaks straight in on cotton, linen and viscose; slowly on wool and silk; and sits on the surface on polyester, nylon and anything with a water-repellent finish.
3. Do the crush test.Squeeze a handful hard for ten seconds and release. Linen and viscose stay creased sharply. Cotton creases moderately. Wool springs back almost entirely. Polyester and nylon barely crease at all — this alone separates most synthetics from most naturals.
4. Do the stretch test.Pull the fabric on the bias. A knit stretches in every direction; a woven stretches only diagonally. Anything with unusual recovery in one direction has elastane in it.
5. Set up the burn test safely.Pull a single thread, ideally several centimetres of it, from an inside seam allowance where the loss will not show. Hold it in tweezers over a sink or a ceramic dish, well away from the garment, with water to hand. Never burn the garment itself.
6. Read the flame and the smell.Cellulose — cotton, linen, viscose — ignites readily, burns steadily with a yellow flame, smells of burning paper or leaves, and continues to glow after the flame is removed. Protein — wool, silk — burns slowly, self-extinguishes when the flame is removed, and smells unmistakably of burning hair.
7. Read the residue.This is the most reliable indicator. Cellulose leaves a soft grey ash that crumbles to nothing. Protein leaves a brittle black bead that crushes to powder between your fingers. Synthetics melt as they burn, shrink away from the flame, and leave a hard bead you cannot crush.
8. Separate the synthetics from each other if you need to.Polyester gives a sweetish chemical smell and a hard black bead. Nylon smells faintly of celery or boiled beans and gives a hard grey or tan bead. Acrylic burns fiercely with an acrid smell and leaves an irregular hard black residue. Elastane, present only in small amounts, smells sharp and chemical.
9. Test a blend by testing several threads.A blend gives you mixed evidence: some ash and a bead, or a paper smell alongside a chemical one. Where you get a mixed result, treat the fabric as containing the more fragile fibre.

Tips

• Warp and weft can be different fibres in a woven fabric — a cotton warp with a polyester weft is common. Pull one thread from each direction and test both.
• A finish can lie to the water test. A cotton fabric with a water-repellent finish will bead water like a synthetic; the burn test is not fooled.
• If you cannot bring yourself to burn anything, the crush test plus the water test will get you to the right care regime in almost every case.
• Never burn a fabric with an unknown coating, a metallic thread or a flame-retardant treatment — the fumes are the risk, not the flame.

Common mistakes

• Burning a piece of the fabric rather than a single pulled thread — A larger sample flares, and a melting synthetic drips. A single thread gives the same information with a fraction of the risk.
• Judging by feel alone — Modern polyester is engineered to feel like cotton, silk and wool, and it is convincing. Feel narrows the field; it does not settle it.
• Skipping the residue and reading only the smell — The residue is the most reliable single indicator. Ash, crushable bead and hard bead map cleanly onto the three fibre families.

Questions people ask