Shirasu is attributed with the stable generation of minus (negative) ions. Indoors, it makes it possible to produce minus (negative) ions equal to the amount found in highland or forest environments. It is incredibly refreshing and comfortable. ■Generating minus (negative) ion 　 Measurement place Minus ion Interior finish material max value min value Average Floor Wall Ceiling Ｕ Residence Wooden Two Floor construction Japanese-style room (The first floor) 1270 780 1025 Mat (Tatami) Satsuma-Nakagirishima-Kabe China plywood Living Room (The first floor) 340 240 290 Flooring Japanese red pine board PB groundwork EP Reference：Amount of minus ion in Japanese various places Nihonbashi Office Bldg.（Average in daytime）:34／Shinjuku skyscraper(reception room of the 30th floor):28／Nobeyama-shi, Nagano Pref.（Air）:115／ Nasu-Kougen, Tochigi Pref.（Air）:692／Offshore of the Pacific Ocean（Strong wind inside）:830