I bought this a few years ago and used it a few times. It's not the latest model. A training mask designed to correct breathing and provide respiratory load for a wide range of users, including top athletes. ReBNA Mask Clear Black L Set includes: Outer mask x 1, Inner mask x 1, Normal valve x 1 set "Breathe again!" With this keyword, the "ReBNA" is a mask-type training gear for nasal breathing, researched and developed through industry-academia-government collaboration. By creating two separate inhalation and exhalation chambers (double chamber system) within the airtight mask, the structure allows for inhalation only through the nose and exhalation only through the mouth. This is a nasal breathing training mask equipped with a valve to resist breathing, suppressing the disadvantages of mouth breathing and promoting nasal inhalation. ReBNA is currently attracting attention in the sports industry. It is used by professional martial artists, professional baseball players, J-League players, keirin cyclists, and medical institutions. ReBNA, which allows users to master the breathing techniques of their specialized sports, is widely used not only by athletes but also by musicians and mountaineers. Type...Other