So next time I need to try this at the laundromat, where the dryers have a glass panel in the door, and I can watch the socks being consumed, and try to gauge the volume ratios.

Seb:

I wouldn’t dare to let two of those things spend much time together. They might join to form a nonorientable surface that would eat more than just socks.

It’s possible the socks tumble more freely when they’re outside the duvet cover than they do when they’re inside — i.e., they contact (and cling to) the duvet cover on just one side when they’re outside, but on both sides when they’re inside — so they move more easily in than out. Alternatively, perhaps the duvet cover billows while tumbling so that there’s more sock-occupying volume inside than out. The socks’ Brownian motion gives them an equal probability of being anywhere inside the dryer by the end of the cycle, but most of that volume is inside the duvet cover. What you’re seeing is the collapse of the wave packet….