Refers to plain-weave thin cotton cloth. The texture of calico is uniform and beautiful. The fabric does not obstruct the movement of the foot, so it is used for the instep of Japanese split-toe socks. The high-quality product is very finely woven, and it does not leak easily even if water is put inside the sock. The sock sole is not made of calico but a twill cloth called "Unsai-ori", which often appears to have diagonal lines.