I saw some of those, as well as expensive battery-heated slippers, but I think Qiao would find it inconvenient, having to recharge them fairly often. Although... the microwaveable ones would have to be reheated even more often, plus they aren't really intended for walking in, and microwaving them too long could ruin them.

Now you've got me reconsidering the battery-heated slippers I saw yesterday. I think it was mainly the price that put me off, though the idea of walking around with lithium batteries by one's feet makes me uneasy too (especially after recently watching a hoverboard burst into flames.)