The Burn Test – Setting Yarn on Fire

Setting yarn on fire might seem odd, but The Burn Test is a way to identify what your yarn is made from. If you have lost a ball band and want to find out if this mystery skein is cotton, wool or acrylic, knowing how each one burns gives you a quick easy and convenient way to find out.

And besides that, it’s fun. In the past I’ve looked at soaking yarn in bleach, and soon I plan to create a post about soaking yarn in water. A little kitchen science with yarn is an enjoyable way to spend an afternoon. But on a deeper level than that, the more we understand our yarn – what its made from, how to Ts made, what properties that gives it – the better the results we can get from our crafting.

So, lets cut to the chase. What is the burn test, and what happens when you set yarn on fire?

Expectations

Wool is animal hair. It should be reluctant to burn, and smell like burning hair.

Cotton is plant fibre. Like wood. It should burn slowly, without a bad smell.

Acrylc is a petroleum based fibre. It should burn well, melt and smell a bit noxious.

Is this what happened?

Setting up The Burn Test

Materials and preparation

I used a flat metal fire proof dish to burn the yarn in, and assembled yarn of different types to experiment with. In addition, I had matches, scissors, and a handy dish of water (just in case, it was never needed)

The burn test on cotton

The strand of cotton caught quickly when I was holding it in the air, but extinguished immediately when I placed it in the dish to photograph.

It burned without any noticeable smell, and left no residue behind. A temporary scorch mark was left on the metal dish (which wiped away with a wet cloth) but no noticeable ash.

The burn test on wool

The pure wool burned brightly when held in the air above the match, but extinguished as soon as I dropped it into the dish. As expected, it smelled just like burning hair. It left behind a very small amount of ash.

Overall, there wasn’t a huge difference between the way the wool and the cotton burned. From my reading on the subject, I had an idea that wool is the most reluctant fibre to burn. It is traditionally used in fire blankets to extinguish flames, after all. And yes, it caught fire when I held it in a flame, and went out quickly afterwards once I removed it from the flame. But so did the cotton. It’s true that a greater length of the cotton strand seemed to have burned. But it’s also worth bearing in mind this is a quick and casual kitchen experiment, not a science lab experiment. So I hadn’t taken accurate measurements of the exact length of yarn strands I was using, nor the precise nano-seconds they were held in the flame.

So, the burning question. (Pun intended). Does wool burn more slowly and reluctantly than plant materials? From this mini experiment I can’t say. What I saw didn’t exactly contradict anything I had read. It didn’t totally reaffirm it either, but that was likely the very basic playful nature of my little kitchen science experiment.

The burn test on acrylic

In the first moment of holding a strand of acrylic above a lit match, there did not appear to be a noticeable difference. It caught fire. It flamed up. Just like the other two.

Undoubtedly however, it burned longer after I dropped it down into the dish. I didn’t notice any particular smell, which was probably because like with the other strands, I only allowed it to burn for a few seconds. The main sources on the burn test suggest that burning acrylic should produce an unpleasant smell.

What was very noticeable was the ash left behind. The acrylic didn’t disappear to nothing when burned the way the cotton and wool had done. Instead, it left behind a thick black residue which took up almost s much space as the strand of yarn itself. Within moments this solidified to become black beads of plastic that I could pick up (with the tip of my scissors, I wasn’t touching that burned plastic!)

What about mixes?

I also burned two other strands of yarn. One was a ‘superwash’ wool, and one was a mix of recycled wool and recycled polyester. This is where the burn test comes into its own. If you have a yarn and aren’t sure of its fibres, burning a small snip will give some information.

In this case. the Reborn recycled wool burned with a bad smell, and left a large plastic residue.

The super wash wool also left a small residue and didn’t leave the clean hint of ash that the pure wool left. This isn’t surprising. The ‘superwash’ process is a method of putting a microscopic acrylic type coating around the wool. When burned, that tiny coating had a disproportionate effect. If I hadn’t read the ball band, and been assessing only on the burn test, I would have guessed that there was a higher proportion of acrylic in the super wash wool than there actually was. An interesting reminder that ‘100% super wash wool’ and ‘100% wool’ are not the same thing!

Why is any of this important?

The burn test can tell us a little about what our yarn is made from, if we need to identify a charity shop haul that came without ball bands. That’s probably the way it’s used most.

But the burn test also shows us in a visual way the different between clean, natural fibres, and those made from plastics, which revert to a more obvious plastic form when burned.

And finally, they tell us something about fire safety. Acrylic is a popular material for making baby blankets, and I personally would never do so. This is one reason. Accidents happen. Flame will not travel up a wool or cotton blanket the way it will up an acrylic blanket. And even if it does, the wool and cotton won’t melt onto the baby’s skin. Wearing acrylic in a fire can cause more serious burns.

I hope you enjoyed this blog post, and gained some value from it. Sign up for my newsletter to be notified of future posts, and receive a free sock knitting pattern today!