Brand new, unused S size 【Semi-permanent Reusable】 Our cool neck ring uses the latest "PCM material" and freezes when the temperature drops below 28 degrees Celsius. When the temperature exceeds 28 degrees Celsius, it absorbs heat and slowly melts while providing a cooling sensation. Once melted, it can be quickly frozen by placing it in cold water or a refrigerator, making it eco-friendly and semi-permanently usable. 【Cooling and Active in Various Summer Situations】 It's very useful in many situations such as camping, walking, jogging, mountain climbing, fishing, indoors, fireworks displays, watching sports, and in the office.