[Warmth on a Cold Night]

The feet tend to get cold easily because they are located farthest from the heart, and according to the ancient Oriental medicine, keeping the head cool and warming the feet, which tend to get cold easily, will improve the circulation of blood and help you have a good sleep.

Do you use a yutanpo? Yutanpo was introduced from China in the Muromachi period. In Japan, it is said that Tsunayoshi Tokugawa used a dog-shaped yutanpo.

Most of the yutanpo of the Edo period were made of copper, which did not become popular among the common people because the material was expensive and they could not easily prepare hot water to keep warm. Ceramic yutanpo did not become popular until the Meiji era, and corrugated tin yutanpo became popular in the Taisho era, but during the war, metal became valuable, so ceramics came into use.

Today, there are yutanpo made of various materials such as metal, plastic, and rubber. Ceramic is characterized by its low thermal conductivity and retains heat for a long time without drying out. You can reuse the used hot water for washing your face, dishes, or watering plants. Feel the warmth of the hot water bottle on a cold night, and enjoy a comfortable sleep.

Ceramic Japan's yutanpÖ
https://www.shokunin.com/en/ceramicjapan/yutanpo.html 

References
https://ja.wikipedia.org/wiki/湯たんぽ
https://www.bioweather.net/column/kotowaza/gw16.htm