Fabric Identification Key
The burn test tells you the family, not the fibre. It cannot separate cotton from linen from rayon — they are the same material chemically.
Before you light anything
Use a snippet the size of a fingernail, held in tweezers, over a sink, with nothing flammable nearby and long hair tied back. Acetate drips while burning — that is the one that catches people out. If the fabric is on a garment you care about, take the sample from a seam allowance or a hem.
What did it do?
The burn test tells you the family, not the fibre
Almost every burn-test chart lists cotton, linen and rayon as separate rows with separate descriptions. They are not distinguishable this way, and the descriptions are the same, because all three are cellulose — chemically the same material in different physical forms. They ignite readily, burn fast with a yellow flame, smell like burning paper and leave a soft grey ash. All of them, every time.
| Family | Near the flame | In it | Out of it | Smell | Left behind |
|---|---|---|---|---|---|
| Cellulose (plant) | Does not shrink away. Scorches. | Ignites readily and burns fast with a steady yellow flame. | Keeps burning, and often glows at the edge afterwards. | Burning paper or leaves. | Soft, light grey ash that falls apart when touched. |
| Protein (animal) | Curls away from the flame slowly. | Burns slowly and reluctantly, sputtering. | Self-extinguishes almost immediately. | Burning hair or feathers. Unmistakable. | A dark, brittle bead that crushes to powder between the fingers. |
| Thermoplastic (synthetic) | Shrinks and curls AWAY from the flame before touching it. | Melts as it burns, often with black smoke. | Usually self-extinguishes, sometimes continues. | Chemical, sweet or acrid. Nothing like paper or hair. | A hard bead that cannot be crushed and cools shiny. |
| Acetate | Melts before it reaches the flame. | Burns AND melts at the same time, and drips while alight. | Continues burning. | Sharp and vinegary — acetic acid. | A hard, dark, irregular bead. |
The single most useful signal is the one you cannot photograph: which way it moves as the flame approaches. Synthetics shrink and curl away before contact. Natural fibres do not — they sit there and scorch.
Where the burn test stops, and where it does not
| Family | Fibres in it | Can burning tell them apart? |
|---|---|---|
| Cellulose (plant) | Cotton, Linen, Rayon / viscose, Lyocell / Tencel, Hemp | No — you need a different test |
| Protein (animal) | Wool, Silk | No — you need a different test |
| Thermoplastic (synthetic) | Polyester, Nylon / polyamide, Acrylic, Elastane / spandex | Yes |
| Acetate | Acetate | Yes |
Note that this cuts both ways. The plant and animal fibres genuinely cannot be separated by burning — but the synthetics can. Polyester smells sweet, nylon smells of celery, and acrylic burns much more readily with an acrid smell. So "the burn test never identifies a fibre" would be as wrong as the charts that claim it always does.
The tests that finish the job
These need nothing but water and your hands, and they are what the charts leave out.
| Fibre | Family | How to tell it apart | Feel |
|---|---|---|---|
| Cotton | cellulose | Stays strong when wet. Creases softly and the yarn is even along its length. | Soft, matte, cool at first then warms. |
| Linen | cellulose | Creases hard and sharply, and the yarn has visible slubs of uneven thickness. | Crisp and cool, softening with washing. |
| Rayon / viscose | cellulose | LOSES most of its strength when wet — a damp thread pulls apart easily. This is the test. | Slippery, drapey, cool. Often mistaken for silk by feel. |
| Lyocell / Tencel | cellulose | Holds wet strength far better than rayon, but not quite as well as cotton. | Very smooth and drapey, similar to rayon but firmer. |
| Hemp | cellulose | Like linen but coarser, with a slight sheen and heavier hand. | Stiff and rough when new, softens considerably. |
| Wool | protein | Springs back from a crease. Visibly crimped fibres if you pull one out. | Warm, slightly springy, sometimes prickly. |
| Silk | protein | Warm to the touch, faintly rustles when crushed, and a single filament is very long. | Smooth and warm, unlike rayon which feels cool. |
| Polyester | thermoplastic | The commonest synthetic. Hard round bead, sweetish smell, black smoke. | Slightly slick, does not crease, warms quickly and stays warm. |
| Nylon / polyamide | thermoplastic | Smells of celery or burnt plastic rather than sweet. Bead is grey-brown and tough. | Smooth, strong, slightly elastic. |
| Acrylic | thermoplastic | Burns more readily than polyester, with an acrid smell and a hard black irregular bead. | Wool-like, warm, lightweight. Pills badly. |
| Elastane / spandex | thermoplastic | Never found alone — always a few per cent blended into something else. | Adds recovery. If the fabric snaps back sharply, it is in there. |
| Acetate | acetate | The vinegar smell is conclusive, and it dissolves in nail varnish remover. | Silky and crisp, with a sharp sheen. Creases and holds the crease. |
The wet-strength test is the important one. Pull a thread out, wet it, and try to break it. Rayon loses most of its strength when wet and parts easily; cotton does not; linen is actually stronger wet than dry. It costs nothing, needs no flame, and it is the only reliable way to separate the three fabrics people most often confuse — which is also why so many rayon garments are labelled dry-clean-only.
An ambiguous answer is the normal answer
Most fabric sold today is blended, and a blend reads as neither parent. A poly-cotton burns, smells of paper, and leaves a hard bead in a soft ash — a combination that matches no single row in any chart. If your results contradict each other, that is not a failed test. It is the test telling you there is more than one fibre in there, which is useful information in itself and the most likely thing to be true.
How to use
- Use a tiny snippet in tweezers, over a sink, nothing flammable nearby.
- Watch what it does BEFORE it reaches the flame — that is the best signal.
- Use the burn test for the family, then a wet thread for the fibre.
- Expect an ambiguous answer: most fabric is blended.
Frequently asked questions
How do I identify an unlabelled fabric?
Burn a tiny snippet to find the family, then use a non-burn test to find the fibre. The flame sorts fabric reliably into plant, animal, synthetic and acetate. Within the plant and animal groups it cannot go further, and that is where a wet thread or a crease test takes over.
Can a burn test tell cotton from linen from rayon?
No, and almost every chart online implies otherwise. All three are cellulose — chemically the same material in different physical forms — so all three ignite readily, burn fast with a yellow flame, smell like burning paper and leave a soft grey ash. The descriptions in those charts are identical because the behaviour is identical.
How do I tell rayon from cotton then?
The wet-strength test, and it is the most useful non-burn test there is. Pull out a thread, wet it, and try to break it. Rayon loses most of its strength when wet and parts easily; cotton does not. It is also why so many rayon garments are labelled dry-clean-only — the fabric is genuinely weak when wet.
How do I tell linen from cotton?
Linen creases hard and sharply where cotton creases softly, and the yarn has visible slubs of uneven thickness running along it. Linen is also stronger wet than dry, which is the opposite of rayon and a useful confirmation if you have already done the wet test.
What does the burn test actually tell me?
The family, quickly and reliably. Plant fibres burn fast and leave soft ash. Animal fibres burn reluctantly, smell of burning hair and self-extinguish. Synthetics shrink AWAY from the flame before touching it, melt, and leave a hard bead. Acetate does both at once and smells of vinegar.
What is the most reliable single sign?
What the fabric does as the flame approaches, before contact. Synthetics shrink and curl away from the heat; natural fibres sit there and scorch. It happens in the first second, it needs no smelling or poking, and it separates the two halves of the fibre world immediately.
Can the burn test identify any fibre exactly?
Yes, some. The synthetics genuinely are separable by burning — polyester smells sweet, nylon smells of celery, and acrylic burns much more readily with an acrid smell. Acetate is conclusive on its own because nothing else smells of vinegar. It is only the plant and animal families where burning cannot finish the job.
How do I tell wool from silk?
Not by burning — both smell of burning hair, both self-extinguish, both leave a crushable dark bead. Use your hands instead. Wool springs back from a crease and its fibres are visibly crimped; silk is warm to the touch and rustles faintly when crushed.
Why does my fabric give a contradictory result?
Because it is a blend, which is what most fabric sold today is. A poly-cotton burns, smells of paper, and leaves a hard bead in a soft ash — a combination matching no single row in any chart. An ambiguous result is not a failed test; it is the test correctly telling you there is more than one fibre present.
Is the burn test safe?
It is if you treat it properly. Use a snippet the size of a fingernail held in tweezers, work over a sink with nothing flammable nearby, and tie long hair back. The one to watch is acetate, which drips while still burning. If the sample is from a garment, take it from a seam allowance or hem.
How can I tell silk from rayon?
By temperature, oddly. Silk feels warm to the touch and rayon feels cool, even though they look and drape similarly — which is exactly why rayon was invented and marketed as artificial silk. The wet-strength test confirms it, since rayon goes weak when damp and silk does not.
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