What Is This Fabric? A Guide to Detecting Textile Fibers (Without Losing Your Mind)

There comes a time in every dyer’s life when you’re staring at a piece of fabric, wondering:

What in the world is this made of?

Maybe you found it in a dusty corner of your stash, or someone lovingly gifted you “a natural fabric” with no label. (Spoiler alert: “natural” is often wishful thinking.)

Before you reach for your dye pot, it helps to know what you’re working with.

Wool doesn’t behave like cotton. Silk doesn’t react like viscose. They all need different mordants. So how do we figure it out?

Let’s go over a few tried-and-true methods, all doable from home (preferably not in your nicest shirt or near open bottles of wine).

1. The Burn Test (a classic for a reason)

Burn Test

Burning tiny snippets of fabric can tell you a surprising amount. Do this in a safe space with good ventilation, and keep water nearby just in case your “tiny snippet” gets ambitious. Especially synthetics can melt and stick to your table, so choose your spot wisely.

Here’s the cheat sheet:

Fiber	Burn Behavior	Smell	Ash/Residue
Cotton	Burns quickly, steady flame	Paper-like	Light, gray ash
Linen	Like cotton but slower	Paper-like	Light ash, slightly more brittle
Wool	Burns slowly, self-extinguishes	Burning hair (truly awful)	Crumbly, black ash
Silk	Similar to wool but finer	Burning hair	Small, crispy ash
Viscose/Rayon	Burns fast, like cotton	Slightly chemical, faint	Soft ash
Polyester	Melts, shrinks, may flare up	Sweet plastic	Hard bead of melted plastic
Nylon	Melts, may drip	Celery or plastic-ish	Hard bead
Acetate	Melts rapidly, flashes like cellophane	Vinegar-ish	Hard bead, sometimes sticky

Pro tip: Polyester blends will often burn with both ash and a hard bead. Welcome to the confusing world of "natural-looking synthetics."

2. The Bleach Test (slow but revealing)

This one takes longer, usually a few hours to overnight, but it’s great for telling the difference between plant-based and protein-based fibers.

Here’s how:

• Take a small swatch of the mystery fabric.

• Place it in a glass jar with a strong solution of household bleach. (MARK THESE AND KEEP AWAY FROM CHILDREN AND PETS)

• Check after 4–6 hours, then again at 24.

Results:

• Wool and silk will dissolve completely or disintegrate into mush. Because bleach destroys proteins.

• Cotton and linen may weaken a little but will generally hold their shape.

• Synthetics often laugh in the face of bleach—no reaction at all.

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Note: If nothing happens after 24 hours, chances are it’s at least partially synthetic.

3. The Feel Test (aka petting your fabric)

This is less scientific, but it gets easier with experience—and sometimes all it takes is a good rub between your fingers.

• Cotton feels soft, sometimes stiff if it’s unwashed or tightly woven. It’s neutral to the touch, neither especially cool nor warm.

• Linen is crisper, with a dry “rustle” and a slightly grainy texture. It stays cool and breathable, which is why it's such a summer favorite. It doesn’t warm up easily.

• Silk has a cool, soft hand and often a subtle shimmer. Here's the magic: it adapts to your body temperature. It warms up quickly in your hands and never feels clammy. Once you know it, you’ll recognize it instantly.

• Wool feels (and sometimes smells)... like a sheep. It’s fuzzy, often springy, and tends to warm up quickly with body heat. Cozy by design.

• Viscose/Rayon drapes beautifully, feels cool and slinky, almost “wet.” It doesn’t adapt to your temperature the way silk does, but it tries to fake it.

• Synthetics vary wildly, but here are a few red flags: it squeaks, it builds static, it feels “icy” in a weird, plasticky way. And it usually doesn’t change temperature much when held, it just stays cold or clammy.

Tips for Labeling and Avoiding Future Guesswork

• Label everything when you get it. Even if you’re “definitely going to remember.” You won’t. (Ask me how I know!)

• Safety pins and scraps of masking tape with fiber content + origin work wonders.

• Store like with like. Create a “mystery fabrics” bin for your test subjects (every textile studio has one).

• When in doubt, don’t dye a whole batch. Test first. Always.

One Last Word

Fiber content matters. It affects how your dye bonds, how long your work lasts, and whether your beautifully dyed shawl melts under a hot iron. But don’t stress, test a bit, keep notes, and treat every piece of cloth like a conversation. Some whisper, some shout, and some you’ll only understand after a few burns.

(Just like people, really.)