81 percent had a kotatsu, though they are warmed using electricity instead of glowing coals or charcoal. Thus, the kotatsu became completely mobile with electricity and became a common feature of Japanese homes during winter. Types There are two kinds of kotatsu used in Japan today, differing in the configuration and the type of heating: Electric: The modern style of kotatsu, , consists of a table with an electric heater attached to the underside of the table. This evolved from a clay pot with hot coals placed under a table. The kotatsu usually is set on a thin futon, like a throw rug. A second, thicker blanket is placed over the kotatsu table, above which the tabletop is placed. The electric heater attached to the underside of the table heats the space under the comforter. Charcoal: The more traditional type is a table placed over a recessed floor, . The pit is cut into the floor and is about 40 centimeters deep. A charcoal heater is placed somewhere in the pit's floor, walls, or, as in the modern-style kotatsu, attached to the table-frame. There are pit-type kotatsu with an electric heater too. Use In the twenty-first century, the kotatsu typically consists of the electric heater attached to the frame, which is no longer limited to wood, but may be made of plastic or other materials. Generally, a blanket (or shitagake) is draped over the frame and heater and under the table-top. This first blanket is covered by a second heavier blanket, known as a (). A person sits on the floor or on zabuton cushions with their legs under the table and the blanket draped over the lower body. The kotatsu was designed when people most commonly wore traditional Japanese style clothes, where the heat would enter through the bottom of the robes and rise to exit around the neck, thus heating the entire body. Most Japanese housing is not insulated to the same degree as a Western domicile and does not have central heating, thus relying primarily on space heating. Heating is expensive because of the lack of insulation and the draftiness of housing. A kotatsu is a relatively inexpensive way to stay warm in the winter, as the futons trap the warm air. Families may choose to concentrate their activity in this one area of the house in order to save on energy costs. In the summer, the