A is a type of mat used as a flooring material in traditional Japanese-style rooms. Traditionally made using rice straw  to form the core, the cores of contemporary tatami are sometimes composed of compressed wood chip boards or polystyrene foam. With a covering of woven soft rush (igusa 藺草) 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 縁) of brocade or plain cloth, although some tatami have no edging.