A tatami (畳) is a type of mat used as a flooring material in traditional Japanese-style rooms. 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 standard sizes, with the length exactly twice the width, an aspect ratio of 2:1. Usually, on the long sides, they have edging (heri) of brocade or plain cloth, although some tatami have no edging.

from Tatami (Wikipedia) CC BY SA 3.0