How to Tell If Yarn Is Wool or Acrylic

The burn test, step by step

This takes two minutes and settles the question definitively. Do it over a sink, with a bowl of water next to you.

1. Cut a 4-6 inch length and untwist it slightly so the fibers can catch.
2. Hold it with metal tweezers, never your fingers, over a ceramic dish or a sink.
3. Bring a flame to the end slowly and watch what the fiber does as it approaches - some fibers shrink away before they touch it.
4. Hold it in the flame for two seconds, then pull it out. The behavior after you remove the flame is the most useful observation.
5. Smell the smoke, by wafting it toward you rather than putting your face over it.
6. Let the residue cool, then press it. Crumbly or hard is the final piece of evidence.

The chart

Reading the result

• Smelled like burning hair and left something you can crush? Wool or another animal protein fiber - alpaca, mohair and silk all behave the same way, because they are all protein. This test cannot tell them apart.
• Melted into a hard bead you cannot crush? A synthetic. Use the odor to narrow it: fishy is acrylic, celery is nylon, sweet is polyester.
• Burned fast and left gray ash? A cellulose fiber - cotton, linen, rayon, bamboo viscose. Again, this test cannot separate them.
• Did both? It is a blend, and that is the most common result in practice. A wool-acrylic yarn chars in places and beads in others, and you will smell both. Wool-acrylic blends covers what to expect from those.
• Self-extinguished immediately? Strong evidence for wool. Protein fibers have a high ignition temperature and stop burning when the flame leaves. This is also why wool is the safer fiber around open flame.

Three tests with no flame

Sometimes you cannot spare a length, or you are testing a finished garment, or a flame is simply not practical. These are less conclusive and they are usually enough to separate wool from acrylic.

The felt test has a known false negative: superwash wool is treated specifically so the scales cannot interlock, so it will not felt and will look like acrylic on this test. If the hot-water test says sheep and the felt test says nothing, you are almost certainly holding superwash wool. Superwash vs non-superwash explains the treatment.

Why it is worth knowing

1. Care. An untreated wool garment put through a hot machine wash is destroyed permanently, and nothing recovers it. Does wool yarn shrink covers what actually happens.
2. Blocking. Wool blocks and holds the new shape; acrylic does not block at all in the usual sense - heat 'kills' it into a permanent limp drape. Knowing which you have changes your finishing plan entirely.
3. Flammability. Acrylic melts and the molten fiber sticks to skin; wool chars and self-extinguishes. That difference is why wool is the better fiber for anything near a fire and why hand-knit acrylic should not be used as children's sleepwear. The US standard is 16 CFR Part 1610.
4. Substitution. A pattern written for wool will not behave the same in acrylic - the gauge may match and the drape will not.
5. Destash honesty. If you are selling or gifting unlabeled yarn, the recipient needs to know. 'Probably wool' is not a fiber content.

What this test cannot do

• It cannot give you a percentage. A blend burns like a blend and there is no way to read 80/20 off a bead.
• It cannot separate wool from alpaca, mohair or silk. All protein, all burning hair.
• It cannot separate cotton from linen, rayon or bamboo. All cellulose, all gray ash.
• It cannot tell you the weight. For that, use wraps per inch, which identifies an unlabeled yarn's thickness, or the yarn weight chart.
• It cannot tell you yardage. Weigh the ball and compare against a known yarn of the same fiber and thickness - how much yarn do I need has the method.

Between this page and wraps per inch you can recover almost everything a lost ball band contained: fiber family, thickness, and from those two the needle size and gauge range. The one thing you cannot recover is the dye lot.