Large futon - Obuton

...Furthermore, toward the end of the Edo period, a rectangular nightgown without a collar or sleeves was invented. This had a frame-like border around all four sides, and because it was the same shape as the bedding used as a futon (until the end of the Edo period, the bedding also had the same frame as the upper mat), it was not called a nightgown but a futon or large futon, and the bedding itself came to be called a futon. However, in reality, only a small proportion of people were able to use such bedding, and most rural areas used bedding made from straw, straw mats, straw mats, rice husks, and in mountain villages, bedding made from fiddler bark, rattan, or hemp waste, and in fishing villages, bedding stuffed into hemp bags with seaweed was used. ...

*Some of the terminology that refers to "large futon" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…さらに幕末になると，衿，袖のつかない長方形の夜着が生まれた。これは四周に額縁のような縁をつけたもので，敷具の蒲団と同じ形であるために(幕末までは敷蒲団も上蓆と同じ額縁つきの形であった)，夜着とよばず掛蒲団とか大蒲団とよび，敷くほうは敷蒲団とよぶようになった。しかし実際にはこうした寝具を使えたのはごく一部で，大部分の農村では薦や蓆，藁（わら），藁叺（わらかます），籾殻，山村ではマダ(科（しな）)の樹皮や籐，苧屑（おくそ）を詰めた夜衾，また漁村では海草を麻袋に詰めるといった，原始時代以来の寝具が使われていた。…

※「大蒲団」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報