It’s a comforter. A comforter in foreign countries is usually relatively-flat because the room air temperature is stable with the central heating. However, in Japan, there are few homes with central heating, so the type or thickness of futons needs to be changed with the seasons. So a kake-buton filled with the thick cotton battings with the high ability to retain heat is used in winter. On the other hand, a kake-buton which is flat and smooth to the touch is used in summer. A coverlet designed for kake-butons is usually used to keep kake-butons clean.