Fabric Fact Friday - KnitsFriday, February 27, 2009Johanna
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.