・The upper layer of non-freezing soft gel remains soft even when placed in a freezer (-20℃), so it fits the head and cools it firmly. The three-layer structure (non-freezing soft gel, hard gel to prolong the cooling time, and insulating sheet) enhances the cooling effect. Can be used repeatedly. Cooling time is 6~10 hours. (The cooling time varies depending on the outside temperature and usage environment.