I should have done this a long time ago, but I only had wool yarn on hand. This bamboo sock yarn is perfect for the purpose. And it doesn't matter if my dyed hair stains them pink!

I have half a mind to decorate the top of the headphones with the same yarn, but I don't know what motif... My embroidery skills are limited. Anyone have ideas? #visiblemending #repaircafe

@Tryllesokker nobody's seemed to ask but how comfortable is it?
@oct2pus The foam is just as squishy as before I added the yarn, and the yarn itself is very soft and smooth. I much prefer this texture over the faux leather it covers up. The yarn is sock yarn, so it has some added elasticity over something like 100% cotton. You could still use pure cotton, but I'm guessing you'd have to be more mindful of the tension. Wool yarn has some natural elasticity too, but I worried it'd be too warm.