How does machine washing a piece of clothing cause it to shrink? what physics and chemistry is behind this?

Answer 1

It is not so much the machine washing as it is heat from the water and the dryer.

You can actually re stretch something that has shrunk, by soaking it in a sink of tepid water and maybe a washer size dose of softener. This will soften the threads and allow you to stretch it back out.

I lay out beach towels to be prepared to lay it out when I am through stretching.

Soak it in the sink until it is thoroughly saturated maybe 1/2 to a full hour. Then gently wring it out. Then over the tub, it's going to drip. Stretch the width and length thoroughly, then lay the garment out on the beach towel . Arrange it exactly as you want it to come out. That should bring it pretty much back to normal. Shrinking makes it sound like a cotton type product. It will probably help as it gets to the barely damp stage, to press it, that will get most of the size back.

Good Luck.

Answer 2

Hot water + certain materials = shrinkage

The dryer is the main culprit, however.