Sleeping Bags for your Feet
First, if you're between sizes, choose the smaller size. I ordered up and had to return them because they were huge! But now, I'm happy.
Super warm, like having sleeping bags on your feet. I learned that wearing socks also and wandering around a hilly little campsite doesn't work well because your foot slides around inside, but they're plenty warm without socks.
In same hilly campsite, crossed a little stream with rocks and slipped, so one Bootie was submerged almost up to the ankle for a moment, and no ill effects. Good as new! Totally happy with these, I'd buy 'em again in a heartbeat.