Can I unshrink a woollen jumper?

Is there anyway to fix a shrunken jumper?
07 March 2017


A woollen jumper



I borrowed my housemate’s woolen jumper and managed to shrink it to half its normal size in the wash… can I use science to get it back to normal?


Chris put this question to Anna Ploszajski from the University College London...

Anna - Yes you can. Now when you shrink a woollen jumper in the wash, what you’re doing is a process called ‘felting.’ To understand felting we have to zoom in and look at what a wool fibre looks like at the micro scale. Wool fibres, funnily enough, have tiny scales on them. Now ordinarily, these scales lie flat against the wool fibre, but what you're doing when you wash your jumper in a hot wash is you’re messing up these scales. So the end up pointing upwards rather than along the wool fibre length and they get snagged on each other, and this is what causes the tangling.

Now anyone who’s ever backcombed their hair will be familiar with felting of hair because this is exactly the same process. So what would you do if you had backcombed hair? Well, you would wash your hair with conditioner to smooth out the fibres again and to get those scales lying down. So this is exactly what you should do with your woollen jumper.

Chris - You condition the jumper?

Anna - Just normal hair conditioner. And if you massage it into your woollen jumper and gently stretch it out, you should find that that will unshrink your woolly jumper.

Chris - Have you tried this? I’ve never heard anyone suggest that - it’s amazing. Does it really work?

Anna - I haven’t tried it but I’ve seen it happen on YouTube.

Chris - Ah well, in that case. It’s rather like these animals with brain freeze. It’s got to be true.

Anna - In that case, it’s definitely true.

Chris - Because there was a gentleman I interviewed a couple of years ago who actually worked out how to unboil an egg. It’s sort of similar in a sense that when put egg into very hot water, you denature the proteins. In other words, you make all of the proteins refold in a way that’s not the normal way they’d fold up to make something egg like and it adopts the cooked egg appearance. If you chemically brutalise that material and heat it up you can rearrange the folding and get it to refold the right way. So you can chemically unboil an egg. Though I wouldn’t advise putting conditioner on the egg but you can, in theory, reverse that process and it’s sort of similar.


Michael - That was a really interesting one because I know a lot of people talk about the concept of entropy in physics and use the idea of an egg being boiled or cooked somehow so you can cook an egg, you can’t uncook an egg because it would bring back order and that’s not what happens in the universe. But the thing that people always miss in those discussions is that the rule in physics is that the entropy of the universe always increases. So you can make something more ordered, so you can then perhaps bring this woolly jumper back to it’s old state by smoothing down all of the scales. But you have to somehow make some disorder somewhere else, perhaps in what remains of the conditioner.

Chris - You know you can, of course, make a woolly jumper with genetic techniques. Because what you do is you cross a kangaroo, from the country I’ve just flown back from, with a sheep you get, of course, a woolly jumper.


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