Used only once. Product Information: For heatstroke prevention in the still-hot weather! Simply put it in your hat to easily cool your head. Uses PCM material, which naturally freezes below 28°C and keeps you cool like an ice pack, maintaining a cooling effect. Just cool it in the refrigerator, freezer, or cold water. No batteries or power needed, and it can be used repeatedly (many times), making it economical. To use, cool the hat pillow in the freezer for about 10 minutes, or in the refrigerator for about 20 minutes, or in cold water for about 15 minutes, and place it on your head before going out, then put your hat on over it. The hat pillow itself is secured when you wear a hat. The cool air goes down, so you can comfortably spend even a short time right after going out. It can be used under hats and helmets, cooling your head and perfect for heatstroke prevention.