To throw in some more information.... Here are some texts from
www.tameshigiri.com Tatami omote is the thin outer covering that is sewn onto the thick rice straw base of the tatami mat. When the cover wears out it is replaced with new tatami omote. The used tatami omote has become the target of choice for tameshigiri in Japan, and the United States.
Tatami omote is not made of rice straw as many people might think. It is made from the stems of a soft rush (juncus effusus) that grows in wetland areas. The stems are collected, cleaned, dried, and tightly woven to make a thin, soft mat. The choice of this traditional material over other materials to make targets for tameshigiri offers an important benefit. Mats made from other, more coarse materials, can scratch the polish on a sword or dull the cutting edge. The ground-in dirt that is found in used mats can also act as a fine abrasive when cutting.
Mat Type Comments
8 Tokutokujo- New Very thick, very expensive, slightly abrasive, and difficult to cut.
7 Tokujo- New Thick, expensive, very slightly abrasive, and difficult to cut.
6 Tokutokujo- Used Very rarely found in the U.S. and a challenge to cut well.
5 Jo- New Expensive to buy new but great to cut.
4 Tokujo and Jo- Lightly Used Most commonly sold "used" tatami in the U.S. (Very Nice)
3 Mugen Dachi Tatami Omote (Nami-New) Brand new Nami grade tatami omote made for tameshigiri.
2 Tokujo and Jo- Heavily Used Another commonly sold "used" tatami in the U.S.
1 Beach Mats Most common material used in the U.S. for tameshigiri (so far)
As a reference for people who are familiar with beach mat makiwara; a target made from three or four beach mats is similar to a target made from one Mugen Dachi mat, a target made from four or five beach mats is similar to a target made from one piece of lightly used tokujo or jo grade tatami.
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So Jake, please believe me... we are cutting something harder here than the majority mats in USA.