To identify a fabric's fiber, cut a small swatch, hold it with tweezers over a metal dish or a sink, light the edge and watch how it burns, smells and what it leaves behind. Cotton, linen and viscose catch quickly, smell of burning paper and leave a soft grey ash; wool and silk burn slowly, smell of burning hair and leave a brittle black bead you can crush; polyester, nylon and acrylic shrink from the flame, melt, and leave a hard plastic bead. Combine the burn test with a water-drop test, a crumple test and a look at the fabric's weave, and you can name most fibers with reasonable confidence.
What do you need for a fabric burn test?
- A swatch about 2–3 cm (1 in) square, or a few threads pulled from the cut edge.
- Metal tweezers or long-handled tongs, so your fingers stay well away from the flame.
- A metal dish, a ceramic saucer or the kitchen sink to burn over.
- A lighter or a long match.
- A glass of water nearby, and a window open.
Keep the test small and short. You are looking at how the fabric reacts, not burning it to the ground.
How do you do a burn test safely?
Burning fabric is a small open flame indoors, so set up properly:
- Clear the area. No fabric, paper, pattern tissue or thread on the work surface, and no children or pets in the room. Tie back long hair and push up sleeves.
- Work over the sink or a metal dish so anything that drops lands on a surface that cannot burn. Melting synthetics drip, and the drips are hot.
- Hold the swatch with tweezers by one corner, never with your fingers, and bring the flame to the opposite edge. Keep the swatch below eye level and away from your face: some fibers flare.
- Move the swatch toward the flame slowly and watch what happens before it touches. Then let it burn for a second or two, pull it away, and watch whether it keeps burning or goes out.
- Smell the smoke from a distance by wafting it toward you with a hand, rather than leaning in. Do not inhale fumes from melting synthetics.
- Drop the swatch into the dish, let it cool fully, then look at and touch the residue.
Test one swatch at a time, and keep the glass of water for anything that keeps burning. If a fabric flares up unexpectedly, drop it into the dish and leave it; do not try to blow it out.
What does each fiber do in a burn test?
| Fiber | Near the flame | In the flame | Smell | Residue |
|---|---|---|---|---|
| Cotton | Does not shrink away | Burns fast with a yellow flame, afterglow | Burning paper or leaves | Soft, feathery grey ash |
| Linen | Does not shrink away | Burns fast, a little slower than cotton | Burning paper or rope | Soft grey ash |
| Viscose, rayon, lyocell | Does not shrink away | Burns very fast, little or no afterglow | Burning paper | Very fine light ash, almost none |
| Wool | Curls away from the flame | Burns slowly, sputters, often goes out | Burning hair | Brittle black bead that crushes to powder |
| Silk | Curls away from the flame | Burns slowly, may go out | Burning hair, slightly less strong | Brittle black bead that crushes |
| Polyester | Shrinks and curls away | Melts and burns, black smoke, drips | Sweet, chemical | Hard, round, dark bead |
| Nylon | Shrinks and curls away | Melts first, then burns, drips | Like celery or boiling plastic | Hard, round, grey or tan bead |
| Acrylic | Shrinks away | Burns fast and melts, sputters | Sharp, acrid | Hard, irregular black bead |
| Acetate | Shrinks away | Melts and burns | Vinegar | Hard, dark bead |
Three families stand out. Cellulose fibers (cotton, linen, viscose, lyocell) all burn like paper and leave ash; the burn test cannot reliably separate them, so use the weave and feel for that. Protein fibers (wool, silk) smell of hair and self-extinguish. Synthetics melt, which is the one thing a natural fiber never does.
Blends show mixed signs. A cotton-polyester shirting burns like cotton but leaves small hard beads in the ash; a wool-nylon suiting smells of hair and leaves a bead harder than wool alone. When you see both ash and beads, treat the fabric as a blend and care for it as the more delicate component.
Which other tests help identify a fabric?
Read the selvedge and the bolt. Before burning anything, look at the selvedge: mills often print the fiber content or their name there. A care label on a thrifted garment is better still. How to read fabric care labels decodes the symbols.
Water-drop test. Put a drop of water on the fabric. Cotton, linen and viscose absorb it within a second or two and the spot darkens; wool absorbs it slowly; polyester and nylon let it bead and sit on the surface, unless the fabric has a wicking finish. A fabric that absorbs instantly and burns to ash is almost certainly cellulose.
Crumple test. Squeeze a handful for ten seconds and let go. Linen creases sharply and stays creased, cotton creases a little less, viscose creases softly, wool and polyester spring back. This separates linen from cotton better than the burn test does.
Feel and warmth. Hold the fabric against your cheek. Wool feels warm at once; silk feels cool then warms; polyester feels cool and slightly slick; cotton feels neutral. With practice this becomes the quickest test of all.
Bleach test for protein fibers. Wool and silk dissolve in household chlorine bleach over several hours; cotton and polyester do not. Put a small swatch in a jar of bleach, cap it, and check the next day. Keep this one away from children and ventilated, and use a jar you will not reuse for food.
Look at the structure. Knowing whether the fabric is woven or knitted, and how, narrows the field: woven vs knit fabric explains how to tell. Cotton jersey, viscose jersey and polyester jersey all look alike until you combine the structure with a burn or water test.
When should you identify the fiber before sewing?
Whenever you do not have a reliable label: thrifted garments and bedsheets, deadstock fabric with a vague listing, inherited stash, remnants sold by weight. The fiber decides how hot you can press (polyester melts under a cotton setting), whether the fabric will shrink and by how much (see fabric shrinkage by fiber), which needle to use, and how the finished garment will feel to wear.
Even when the label is clear, a quick burn test on a scrap before pressing a new fabric is worth the minute it takes. A shirting sold as cotton that leaves beads in its ash is a cotton-polyester blend, and the iron needs to come down a notch.
What are the limits of the burn test?
It separates families, not individual fibers. It cannot tell cotton from linen, viscose from lyocell, or wool from cashmere, and it cannot give you the percentage of each fiber in a blend. Finishes, dyes and coatings can change the smell or the way a fabric catches. Treat the result as a strong clue rather than a certificate, confirm it with the water, crumple and feel tests, and when a fabric is precious, press and wash a swatch first regardless of what the tests say.