Why Do Sweaters Shrink But Sheep Dont?

Why does wool shrink but sheep don’t? Why does wool shrink when you wash it? How do you fix a shrunken sweater?

This question was presented to me on WebAnswers. A person asked “How come sheep don’t shrink when they get wet?”. This line of thinking would come from the fact that when a person has a wool sweater they have to take care when washing it or it does have the risk of shrinking.

The answer is simple really, sheep are living things, it is the wool that shrinks, not the animal beneath the wool. A wool sweater may shrink but it is not made up of “sheep” it is made up of the fleece that the sheep has produced.  Even the wool when on the sheep does not shrink – and of course there is the fact that some sheep do not have woolly fleece at all, they are hair sheep!

Above a Barbado hair sheep ram.  ©Brenda Nelson

Actually what causes a wool sweater to shrink is not so much the washing, but more so the drying. When the wet wool gets hot the fibers naturally cling together, they have a natural crimp that grabs on to the other wool fibers and do not want to let go.

An actual living sheep might get wet, but it does not get hot enough for this to occur. Additionally you have to factor in that when on the sheep the fibers are all growing naturally in the same direction. Sheep hairs are not as smooth as human hairs, they even have minute scales, after being spun into yarn the fibers are all over the place, and the texture of each fiber grabs onto those next to it. If agitated further these fibers can be made into felt. This is why the hair of some animals can be spun into yarn, or made into felt, but you cannot do the same with hair from every animal.

So to get back to why the wool on sheep does not shrink, but the wool in sweaters does, we see that the wool in sweaters is not as well arranged as on the sheep – with the fibers going every which way, when you add water and heat, the fibers grab onto each other, pulling each other together resulting in shrinkage.

Wool sheep, Diamond and Favorite, ©

Sometimes, to prevent shrinkage, wool is treated with chemicals to remove some of these scales, this does result in less shrinkage, but shrinkage in sweaters can also be prevented by not heating up wet sweaters – they can be dried safely with cool air.

If you have accidentally shrunk a sweater you can “un-shrink” it by soaking it in warm water with a bit of hair conditioner added. Pull the sweater gently while it is soaking. Remove from the water and lay flat, pulling gently again relax the hold the fibers have on one and other, and to pull it back into its proper size.

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Published in: Consumer Information

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RSSComments: 9  |  Post a Comment
  1. nice article funny

  2. Happy NEW Year

  3. When I saw your title Brenda, I couldn’t wait to see how you’d deal with it. This is so well done. I can certainly remember teenage years, when wool garments were more in vogue, trying to dry something in a hurry and totally ruining it. Great article here.

  4. Yes, we must remember that sheep are not made of wool.

    Very interesting question though!

  5. Interesting tip on unshrinking a sweater. I’m going to keep that one in the bag to impress my wife down the road. :-)

  6. Great article! (Lovely photos too). I wish I’d known that un-shrink secret when I was a kid…the amount of my favourite woolie pullies that ended up as dolls clothes could’ve all been saved!

  7. Candid question gets a candid answer too. you did answer the questions all too well and you also have presented helpful info on how to take care of wool sweaters.

  8. Interesting question to be answered! Didn’t know you could unshrink a sweater- thanks for sharing!

  9. If you tease a sheeps wool while on the sheep and dry it would it shrink then?

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