When we sleep at night, we normally turn off heaters in winter, so houses get cold. Instead we use yutanpo to warm up our body.
It’s a tank we put boiled hot water and put it in a thick bag, and keep it inside of a bed/futon, usually around feet. It’s important to keep little distance (about 4 inches) to avoid a burn. It keeps you warn entire night.
Yutanpo isn’t inexpensive, and using it is actually an economical way for winter nights rather than using heaters.
One of my friends (Japanese) living in the U.S. uses yutanpo there and she save a heating cost! (She lives in North Chicago)
Orange and silver ones are traditional types of yutanpo in Japan, though now there are so many kinds and color of yutanpo.