Adult Science Amazon Limited Edition Original Sauna Hat Gakken Adult Science Magazine Sauna Watch First Edition Limited Sauna Hat (☆Sa⭐︎Hat) Collaboration with sauna goods brand Blue Amazon exclusive, so it's a rare item and difficult to obtain! Size Free size, depth 25cm, head circumference 60cm Made of microfiber, it's quick-drying and durable, so it seems like it will last a long time.