A futon is a traditional Japanese style of bedding. A complete futon set consists of a mattress (shikibuton, lit. "spreading futon") and a duvet (kakebuton, lit. "covering futon"). Both elements of a futon bedding set are pliable enough to be folded and stored away in a large closet (oshiire) during the day. This allows a room to serve as a bedroom at night, but serve other purposes during the day. Traditionally, futons are used on tatami, a type of mat used as a flooring material. It also provides a softer base than wooden or stone floors. Futons must be aired regularly to prevent mold from developing, and to keep the futon free of mites. Throughout Japan, futons can commonly be seen hanging over balconies, airing in the sun. Futon dryers may be used by those unable to hang out their futon.

Source: Wikipedia