by Katherine Wu

Everyone remembers their first. Their first wool sock lost to the treacherous waters of the washing machine, that is. Wool clothing shrinks when it’s wet – so shouldn’t sheep, which are covered in the same material, shrivel up after torrential downpour?

Yes – and just like your sweaters, the simple household trick of soaking sheep in conditioner and stretching them back out works like a charm. Just be sure you don’t toss them in the dryer after!

… Okay, clearly I’m spinning a yarn. But behind that woolly lie is an actual explanation of why the real answer is: sadly, no.

So, now that I’ve exceeded my pun quota, let’s discuss why wool clothing can sometimes shrink in the wash. This was a much more common phenomenon a couple decades ago, when most wool products weren’t treated and had to be washed in cold water by hand. Now, acknowledging that most people like to machine wash their clothes in big batches, a lot of clothing companies have taken to chemically treating wool so they can be washed with standard detergents on cold cycles. But certain socks and sweaters remain too delicate for anything involving heat, soap, or agitation. Why?

Cotton, a plant product made of complex sugar chains, does just fine in the warm, sudsy water of the washing machine – but wool, much like hair, is made of protein. Unlike hair, however, wool is naturally crimped and elastic, which means the fibers interlock and hold their shape well, trapping air in miniscule pockets; think of wool as an enmeshment of springs with great structural integrity and insulating power. The interlocking power of wool holds true all the way down to the microscopic level: the individual fibers are covered in little shingles that resemble tree bark or wrinkled papier-mâché.

But after processing, these same flaky protrusions are these textiles’ downfall in the wash: after wool is spun, the individual fibers are stretched out beyond their original length and the shingles don’t all orient in the same direction. Now, when the fibers are agitated by warm, soapy water and the friction of the moving laundry load, they will expand, making the scales flare out, snag onto each other, and intertwine, compacting the wool. Some knitters will treat wool this way on purpose in a process called felting – which, shockingly, produces felt.

Luckily for lazy millennials like me, you can now buy wool clothing that has been treated to minimize this flaring, and thus minimize shrinking even in the presence of heat, soap, and agitation. Generally, though, it’s still a good idea to wash your wool products on a more delicate cycle in colder temperatures.

As you may have already guessed, a little fall of rain is not the same as being shoved unceremoniously into a laundry machine – there is simply not the heat, soap, and agitation that would be required to shrink a sheep in a storm. But even if a sheep were to get swept up in a steamy hurricane next to a Tide factory, there are a few more protective measures that would help it keep its shape.

For one thing, because wool on a live sheep hasn’t been processed, stretched, and spun, the scales on the individual fibers all point away from the sheep’s body. This uniformity helps prevent tangling in wool’s natural state, and would guard against the interlocking required to compact the wool fibers after laundering.

What’s more, “raw” wool – which is the term for the stuff sheared straight off the sheep – is almost unrecognizable compared to the wool in our clothing. This is in part due to the fact that sheep are, well, sheep, and their wool is covered in dirt, grease, sweat, field debris, and who knows what else. There’s even a special term for the muck on wool – “suint” – and it can comprise up to 70 percent of raw wool’s weight. To get from this to pure wool suitable for clothing, it must be scoured – basically, scrubbed in a hot, soapy, alkaline bath. In particular, this process rids the wool of lanolin, a wax commonly used in beauty products. Lanolin is the greasy Swiss army knife of wool: its properties 1) prevent fibers from sticking together and tangling; 2) protect sheep skin from the environment; and 3) waterproof wool, which would otherwise absorb rainwater and other liquid and become exceptionally cumbersome.

So even if you put a sheep in a washing machine (let the record show that I do not endorse this), the uniform scales and the lanolin would protect the wool on the sheep far better than the spun, scoured wool in your sweaters.

Anyway, now that summer is in full swing, I’m sure wool is, for many of us, one of the last things we want to pile on our bodies before heading out the door (my education thus far has failed to communicate to me just how much summer in DC is like living inside someone’s armpit).

But come wintertime, once our summer tans have molted and we begin to shake the mothballs out of our holiday sweaters, take care to clean all your clothing only as instructed – because the wool in your sweater is, thankfully, not in the same state it was on a sheep.

Happy laundering! And remember, kids, don’t machine wash sheep.

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Katherine Wu is a graduate student at Harvard University and Co-Director Emeritus of Science in the News.

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