A tatami is a type of mat used as a flooring（床） material in traditional Japanese-style rooms. Traditionally made using rice straw（わら） to form the core, the cores of contemporary（その当時） tatami are sometimes composed of compressed wood chip boards or polystyrene foam. With a covering of woven（織る） soft rush (igusa) straw, tatami are made in standard sizes, with the length exactly twice the width（幅）, 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.