It is a Japanese-style floor with tatami-mats made of rush grass. The size of each mat is 910×1820mm and several pieces of tatami mats are laid all over a floor. In ancient times, tatami-mats were used as shiki-butons, however, people started to sleep on a shiki-buton with the tatami mats after the Heian Period. Tatami-mats are a little hard, however, it is comfortable to sleep on it without shiki-butons for taking a nap. The tatami-mats absorb and release moisture well, so they are suitable floor materials for futons in a humid country like Japan. Also, they have sound insulating properties, so footsteps or the sound of dropping can’t be heard downstairs.