And so on to question four and we’re getting towards the end of this tenth series of Five Questions.
Question 4: Why don’t sheep shrink when it rains?
Because they’re 10% nylon?
But seriously … The real answer is almost certainly to do with the cross-linking of the long-chain protein polymers that make up each hair and the mechanical interlinking between the individual hairs. The more random cross-linking there is, the more the proteins will fold together and the curlier (thus shorter) the hairs. Similarly the more random the mechanical interlinking, the more likely the fibres are to be shorter. Wool has to be processed to remove this interlinking and cross-linking and create straight fibres, which we call unshrunk. Heat, water and mechanical action go to create the randomisation of the linking and thus cause the fibres to shrink in the wash. Now sheep are a natural product; they aren’t processed. Hence their wool is pretty random and effectively pre-shrunk, so they aren’t going to shrink more in the rain.
So the sheep’s coat is more felted than knitted? And then carded before spun? I wondered for a long time why US pea jackets and Navy frock coats didn’t shrink, and I guess felting is what you are describing. I wondered too if sheep are double coated, like a collie, which essentially wears a rain-shedding poncho over felted long underwear.
Yes, I guess that the physical interlinking is how felting works. It’s something I’d not thought about, but it is also the way spinning wool must work. So sheeps’ coats must be at least loosely felted as the wool has to be teased apart (carded?) before being spun — indeed in times gone past weavers did in fact use teasels to do this. But I have no idea whether they have a multi-layered coat, although many animals do including (as you say) dogs and cats.