The Science of Plant Fibers


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Ready for a science lesson?

Probably not. That opening probably sent most readers off to find fresher, less geeky, internet pastures to frolic in. But for the geeky curious who stuck around, let’s get into the science of plants, fibers made from plants, and why yarn made from plants will work up differently.

First plants fibers don’t have scales. Animal fibers do. Its the scaliness of animal fibers that leads to felting. You know how any hair can mat and/or form dreadlocks? That’s the scales of individual fibers locking together and that’s what happens when you felt wool or alpaca.

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Plant fibers don’t have scales and so they will never felt. But… most of us who play with yarn already know that. The other important property of plant fiber yarn is that its hydrophillic.

Once a Plant, Always a Plant

Plants are hydrophillic.

Hydrophillc – a substance that will absorb water

When you teach science stuff professionally you are often warned not to anthropomorphize, not to assign pretend human feelings and characteristics to non-human things, when you explain science stuff. I break that rule all the time. So just think of it like this: hydrophillc substances like water. They open their doors and let the water in.

(Hydrophobic substances don’t let water in. Glass, metal, and most plastics, those are all hydrophobic.)

In plants this hydrophillic action takes place at the cellular level. Plant cells want water and that remains true even after the plant is dead. When you re-hydrate dried vegetables? When a wooden door swells up because its humid? That’s hydrophillia in action. The same thing is at work in plant-based yarns.

Plants that can, and often do, get turned into yarn include cotton, flax, hemp, bamboo, soy, and sometimes nettle. These all have different properties and they yarn reflects those properties but the one thing they have in common is they are made of plant cells.

When a plant is harvested, processed, dyed, and spun into yarn it gets dried out. Some stages of yarn production add water and others take away water but in the end, that plant is drier than it was when alive. Processes that dry plant cells out are called plasmolysis.

But once a plant, always a plant. As long as the cellular structure of the plant is intact, those cells want water. They will never grow again (no matter how much water you pour on your cotton socks they won’t sprout roots for you) but the mechanism that plant cells have to absorb water remains. So add water (science geeks call that a hypertonic solution) and you get de-plasmolysis.

What it Means for Your Yarn

This week I started working with CotLin DK from Knit Picks. Its a blend of 70% Tanguis Cotton, 30% Linen. So its all plant fibers.

Cotlin DK yarn

I’ve never worked with this yarn before. Its a new-to-me (and that is always fun). So first thing I know I have to do is swatch with it. But I have worked with plenty of plant-based yarn in my time and I know that CotLin yarn is hydrophillc. Anytime you work with plant-based fiber expect it to be different after its been wet.

So I swatched, like a good little knitter. Then I washed my swatch, like a smart little knitter. Here are the before and after pictures:

Dry (on the left) and wet (on the right) swatches with CotLin DK yarn

I’m sure you can see that once the swatch was wet, it “grew”. Notice that its not under tension. I’m not stretching or pulling it, its bigger all on its own. That’s hydrophillia for you. In the case of this yarn, CotLin DK, I’m seeing about 10% expansion in both directions.

Would the yarn/swatch shrink back as it dries out. Technically yes it would. As the plant fibers dry, all the cells shrink and the yarn would get thinner. But in practice that doesn’t happen. Once a piece has been knitted or crocheted, its going to get worn. It will pick up moisture from your body and from the air. And it will get washed with some regularity. It will probably never be as dry as it was when you bought it.

What does this mean? Never trust the “dry” gauge of a plant-based yarn. Washing the gauge swatch of any yarn is always a good idea and if you can get into the habit of that you have fewer surprises in your finished pieces. But always-always-always wet block cotton/linen/bamboo before you start a major project. A 10% change in your gauge can really screw you up if you aren’t expecting it.

So there is a little yarn science for ya. That wasn’t overly painful was it?

Its summertime as I write this which means knitters and crocheters everywhere are eyeing those cool, lightweight plant-based yarns. If your making dishcloths then you won’t be concerned much with the hydrophillc expansion of your yarns. But if your using a plant yarn to make something to wear, get that yarn in some water and see what it does.

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30 Comments on "The Science of Plant Fibers"

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Thanks for the reminder! Btw, have you had any experience with plant fibers…especially the longer ones like flax, hemp, bamboo…spin more easily one direction than the other?

Hi Jenn, I found your blog fascinating. Not boring at all. Sorry I haven’t been leaving a reply to your blog as of late. Been really busy packing some household items that are rarely used and storing them in one of the spare bedrooms, and donating others to local goodwill. I’ve also been giving each room a deep cleaning. And although no reply was written, I did read all the blog postings. When all the kids leave the nest, you are left with a lot of items you no longer need or want. You would be surprised with the amount… Read more »
Amy C

Very interesting and extremely useful! I love learning more about knitting and why things are the way they are. Sometimes I’m surprised that I hadn’t thought to question a particular concept. I knew that cotton tends to grow and thought it was just because of not having scales.
Thank you! I also always always read your blog but don’t comment nearly as often as I ought to.


Thank you for your very informative post! I have 2 follow-up yarn questions: Why do some yarns shed and is there a way to minimize the shedding? I have done baby alpaca and don’t know what to do without it because of all the shedding.


That was SO interesting! I never knew that about plant-based yarns. I’ve recently started knitting with bamboo to make baby sweaters and knowing I need to wash my swatch and check for expansion will come in very handy.
I love to get my “geek” on. Thanks for sharing yours with us!