Why Does Wool Shrink & Felt

And other answers to your fiber questions…

Why Wool Felts

Why do wool and other animal fibers shrink and felt but cotton, linen and synthetic fibers don’t? Why are some fibers softer than others? It’s because of the structure of each individual fiber.

This is a microscopic image of several fibers:

Common Fibers Under a Microscope

Why Some Fibers Felt and Shrink

One of the first things you will notice is that the animal fibers are not smooth. When they are agitated, the scales on the animal fibers lock together. That’s what causes felting and shrinking. Fibers with a larger quantity of more pronounced scales are more likely to felt and shrink than those with fewer, smaller scales.

As you can see the coarse and fine wool are the most likely to felt, but alpaca and cashmere will also felt and shrink if agitated enough.

Those scales, along with the crimp (or curliness) of the fiber are what gives animal fibers their “memory”. They hold their shape well. Cotton and linen do not have memory and do not hold their shape well. You may have noticed this if you ever knit a cotton sweater or shawl, only to find that it grew on the hanger.

The one fiber that is missing from this photo is superwash wool. Superwash is a term used to describe wool that has been treated to prevent it from felting and shrinking. There are a couple of processes, and I won’t go into detail here except to say that depending on the process, it either removes the scales or fills them in to create a smooth fiber.

You might think that the scales are what cause a fibre to be itchy. They may be a contributing factor, but the main factor in whether a fiber is itchy or not is the diameter of the fiber.

Why Some Fibers Are Itchy

The itch factor of a fiber is dependent on the thickness of the fiber. The larger the diameter of the fiber, the more itchy it will be. The smaller the diameter of the fiber, the softer the fabric will be. That’s why cashmere is so luxuriously soft – it has a small fiber diameter.

An example is the best way to illustrate this…

If you poked yourself with a blade of grass, the grass would bend and you would barely feel it. If you poked yourself with a toothpick, it would not bend and you would feel the poke.

The same idea works with fibers. The thicker the fiber, the less likely it will bend when it touches your skin. The itchiness you feel is those fibers poking your skin.

Why Some Fabrics Pill

Pilling is a common phenomenon with fine animal fibers. It’s frustrating but unavoidable. However, it can be minimized by buying quality fibers.

Yarn is made of fibers that are twisted together. Pilling occurs when the yarn is made with short fibers. It can also happen in the normal wear of a fabric as the fibers break. The finer the fiber, the easier it will break.

The short fibers are not held into the twist as well as the long fibers. Their ends poke out of the yarn, and that is what forms the pills.

Quality yarns and garments are made with long fibers. I suspect that is the difference between a $60 Sam’s Club cashmere sweater and a $400 Nordstrom’s cashmere sweater. The $60 sweater will feel wonderful, but it will start to pill and wear out long before the $400 sweater.

Know what You Are Buying

You may wonder why some fiber is short and some is long within the same breed.

Animals are just like humans with regard to the quality of their fleece. Some humans have hair and nails that grow fast; some grow slow. Some people have thick hair; some have thin hair. Some people have brittle hair; some have supple hair. The same is true for animals.

Fiber quality is affected by genetics, nutrition, and the overall health of an animal.

The first step in processing a fleece is to determine it’s quality. Fleeces are sorted according to grade, and sold accordingly. Top quality fleeces are used to produce top quality yarns and garments. Lower quality fleeces are used to produce less expensive items and felted products.

This is true for all types of fibers. You wouldn’t use coarse yarns for a sweater, but great quality coarse yarns are used to make very expensive rugs. Lower quality coarse yarns are used to make inexpensive rugs.

If you enjoyed this article and are a knitter, you might benefit from joining the online Mountain Hollow Farm Knit Along Club. Our goal in the Club is to help you become a better, more confident knitter. Each knit along includes written and video tutorials to guide you through every step of the pattern. Click on the graphic below to try it for free!

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