Down booties are a type of footwear. To put it simply, their whole job is to provide insulating warmth during the winter months. Just like a down jacket would keep your core warm or puffy pants would keep your legs warm, down booties keep your feet warm.
You’ll commonly see them worn in places like winter huts, inside four-season tents, or on trips for ski mountaineering, ice climbing, backcountry skiing and touring, winter camping, and more.