Friday, February 27, 2009

Fabric Fact Friday - Knits

Knit samples from my textile science class.

I'm currently taking a university class in textile science. It's mostly a distance course and it's highly theoretical. Sometimes it feels more like I'm taking a chemistry class and my brain has been out of school for so long that I have a hard time grasping all this stuff. Anyhow, I want to share some of the things from the class under this new headline - the weekly Fabric Fact Friday. Hopefully blogging about it will also help me remembering the facts, since I have a big exam in April.

Knit fabric Q&A
Why do some knits shrink when washed?
The cause of the shrinkage is actually swelling. And the more water the fiber absorbs the bigger the shrinkage will be. Cotton for instance can take up 30 percent of water during washing and when the threads are stretched out they react by trying to pull themself together, hence the shrinkage. Synthetics on the other hand only absorbs a very small amount of water, which is why they don't shrink much when washed. Also loosely knitted fabrics will generally shrink more than tightly knitted ones.

Why do fabrics pill?
There are a number of reasons for that. Mostly it's because the fibers aren't long enough, i.e. the manufacturer has skimped on the quality. Actually almost all knitted fabrics pill to a certain extent, but in cotton for instance the small pills just fall off so you don't really notice them. Also blends are more prone to pilling since the fibers often clash. For instance synthetic fibers are stronger than most natural fibers. The result is that the synthetic fibers rubs off from the surface of the fabric, but since synthetics are more resilient the pills doesn't fall off like the cotton ones do.
Another cause of pilling is a loosely knitted (or woven) fabric. The looser the knit, the bigger the risk of pilling.
Fuzzy yarns, like angora and alpaca, are also prone to pilling since those fibers are very loose.

Why do some knits twist when washed?
It's a production fault and is most prevalent on single knit fabrics, such as t-shirt jersey. In order to speed up the production on the round knit machines some manufacturers use too many yarn input places which cause the knitted tube to spiral. This can be tricky to spot, but if the fabric is striped the stripes won't be straight. Another reason for twists is that the fabric is cut open and placed on a frame afterwards which stretches out the fabric. This can cause distortions and when the fabric is washed it retains the original shape - hence a twist in the garment will appear. This makes a good case for prewashing knits before cutting I think.

6 comments:

  1. I cannot overstate enough how helpful this was! I've always wondered why some of my sweaters pilled!

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  2. It's been exactly 39 years since I took a Textile Science class at University, but I have to say I have found it to be probably THE most useful class I ever took in 6+ yrs of 'higher education'...

    Thanks for sharing the info on knits with the blog readers!

    (hope this isn't a duplicate post...)
    Elaine

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  3. Hey this is really interesting, thanks! I had the misfortune of having an amazing dress pill like the third time I wore it (rayon-poly-lycra blend), and at the time, no one on PR could conclusively tell me why, or how to avoid it in future. thanks. (and feel free to post more things you learn in class!)

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  4. Looking forward to the continuing series! I never knew any of these facts before.

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  5. Awesome - I didn't know why some t-shirts do that twisting thing and are impossible to fold well till your post! Looking forward to more Fabric Fact Fridays! :)

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  6. Thanks for pointing out these facts. Now for finding a manufacturer that doesn't skimp... I'm also looking forward to future installments!

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