I bought it last year but don't think I'll use it. Size L (diameter approx. 12cm) Cools your neck with special material (PCM material) that maintains 22℃. Since it maintains 22℃, there is no sudden cooling, and the cool feeling lasts longer. Cooling time is approximately 90-120 minutes (when ambient temperature is 25-35℃). Effectively cools your body by cooling your neck. Easily solidifies in environments below 22℃ (cold water, cold air). It solidifies in environments below 22℃, so it can be easily cooled with a refrigerator or tap water, and can be used repeatedly, making it economical. It can also be cooled in outdoor environments by placing it in a cooler box. Resists condensation! Your clothes and hair won't get wet, so it's comfortable. Recommended for women and children. #IceNeckRing