Tatami (originally meaning “folded and piled”) mats are a traditional type of Japanese flooring . Traditionally made of rice straw to form the core (though nowadays sometimes the core is composed of compressed wood chip boards or polystyrene foam), with a covering of woven soft rush (igusa) straw, tatami are made in uniform sizes. Usually, on the long sides, they have edging (heri) of brocade or plain cloth, although some tatami have no edging.
Tatami were originally a luxury item for the nobility. During the Heian period, when the shinden-zukuri architectural style of aristocratic residences was consummated, the flooring of shinden-zukuri palatial rooms were mainly wooden, and tatami were only used as seating for the highest aristocrats. In the Kamakura period, there arose the shoin-zukuri architectural style of residence for the samurai and priests who had gained power. This architectural style reached its peak of development in the Muromachi period, when tatami gradually came to be spread over whole rooms, beginning with small rooms. Rooms completely spread with tatami came to be known as zashiki (lit., room spread out for sitting), and rules concerning seating and etiquette determined the arrangement of the tatami in the rooms.It is said that prior to the mid-16th century, the ruling nobility and samurai slept on tatami or woven mats called goza, while commoners used straw mats or loose straw for bedding.
The lower classes had mat-covered dirt floors.
Tatami were gradually popularized and finally reached the homes of commoners toward the end of the 17th century.
Houses built in Japan today often have very few tatami-floored rooms, if any. Having just one is not uncommon. The rooms having tatami flooring and other such traditional architectural features are referred to as nihonma or washitsu, “Japanese-style rooms”.