If wool shrinks when its washed, why dont sheep shrink when it rains?

Greg Sek 1371

Hi there Rebekah,
Well I had no real idea myself, so I turned to a real expert in wool science. This is a very popular and important industry in Australia and New Zealand, where a number of good univeristies run degrees in wool science and production...so to there I turned.

Here is the response I recieved from Miss Helen Daily, who is a professional woolclasser and more than qualified to make this response. You can find more information via the Woolwise website:

"The problem lies in the professor's misinformed question. Wool does not shrink, it felts. And this is simply because of the raised scales of the cuticle layer of the fibre catching on one another. The fibres in a fleece on a sheep are all growing out of the follicles in the same direction, and generally speaking, they all grow at a similar rate. This means that the cuticle scales (which are a bit like the teeth on a saw, but not that pronounced) are all pointed in the same direction. They don't catch on one another. These scales can be seen clearly in electron micrographs. (some available on the Woolwise site).

After the fleece is shorn, the processing stages cause the natural fibre alignment to be completely disrupted. As the fleece is scoured, the "staple" structure is destroyed and the fibres no longer line up "tip to base" as they would in the fleece. They can be in all dimensions and also suffer entangling after scouring and drying, and the purpose of subsequent carding and combing is to remove extraneous matter and disentangle and align the fibres into a parallel arrangement. However the fibres will not necessarily be "tip to base". The scales now can be at 180degrees to one another, and can catch on one another.

When the fibres are spun, they come in close contact with each other, and the interlocking nature of the scales is what helps keep the yarn together (apart from the twist that is inserted). Felting usually occurs in the presence of heat, water and agitation, and this acts as a ratchet, tightening the contact between the fibres in the yarn, and then the yarns in the fabric.

Wool's propensity to felt is because of the scales on the fibre. Other animal fibres have cuticular scales also, but to different degrees. For instance, the scales on human hair are much flatter. I don't know much about dreadlocks, but I imagine this is caused by interrupting the usual parallel arrangement of the hair scales. Fine diameter wools are more likely to felt than broad diameter wools because they have a greater surface area, and hence more scales proportionately.

Shrink-proofing is a chemical treatment of wool, which uses chlorine to "burn" off the scales...this doesn't entirely remove them, but it does lessen their profile, and then the fibres are coated with a resin to smooth the fibre still further. This allows the wool to be machine washed without felting, and the shrinkage of the fabric associated with felting. So that is the story of wool felting in a nutshell. The wool proteins are very interesting, but really don't play a role in this part of the wool story!"

Thanks for that Helen!....and I hope that answers your question Rebekah. I certainly learnt something new!

All the best

Jim Caryl
MAD Scientist

References:

Helen Daily at the University of Adelaide & The Woolwise Website.

Milena Petrova 1247

Because rain is cold, durh! If you don't want your garments to shrink, don't wash them in hot water and don't dry them in the dryer... The sheep learned the dryer part the hard way.

Jody Vetter 1224

When you shear a sheep to make wool, the fur is stretched and pulled among other things over and over again to make the wool. Plus all of the natural oils are stripped away. So when heat and water are added later it basically makes the wool want to shrink and stick to its original form. And since its original form was on a sheep, its harder for it to shrink even more if it rains on a sheep.

Jay Mariie 1441

Because they are flesh and blood, not made out of wool. And wool only shrinks if it is woven tightly together into fabric.

aLSO. . .
A sheep's fur has an oil on it called lanoil or something close to that and it coat the fur as a water repellant. If this oil is to wash off it is just replaced by the skin. When the wool is shaved off of them there is nomore oil.

Unknown Brain 1222

Juliet is correct. Sheep do shrink when wet. In Iceland, for example, a place known for both its torrid down pours and its mutton, it is common to find sheep that can stand in the palm of your hand. These tiny sheep are on the top of a fragile ecosystem in which small Icelandic toads feast on wet, shrunken lambs.

Juliet Fitzgerald 1188

They do.

Stas Urban 2168

Simple answere its because the sheeps hair is just like any other animals on the body its is separated into particular strands.Each hair isnt connected to anouther but when you sheer the sheep and make cloths out of it you must band the hairs together to form the string.An because not all the strands of hair are the same length or texture,they contract or expand at different temparatures

Mungo Jerry 1248

for the same reason that you have to be important before you are assassinated instead of just murdered. that's just the way it is

Johanna Painter 1234

Rain water isn't hot and the wool isn't being dryed by a high power machine.

Jake-Stephanie Ham 1259

Because when the wool is on the aminal it is still continuing to grow and is technically still alive