The purpose of the hand warmer was to provide comfort as well as warmth. You removed a piece of charcoal, placed it inside the metal container stuffed with felt, and put it in your pocket. It would radiate enough warmth to warm hands and, for some way, lighten the otherwise bitterly chilly winter days.
In this sense, technology was incredibly beneficial, even though it looks quite archaic now. Charcoal sticks were burned and put into a piece of metal container that was made in a specific way. In order to keep the warmth within while preventing direct heat contact, it was also usual to place felt or another material along the case’s sides.
Not only did the charcoal last for hours, but the ventilation at the back of the case prevented the charcoal from burning out too soon.
