Brand new, unused! Opened for photography! Although it's new and unused, it has been stored at home, so there are some tears and wrinkles in the description. Please purchase only if you can accept this. Size: M It uses a high-elastic TPU outer layer and a PCM phase change cooling inner core. In environments below 28°C, the PCM naturally crystallizes, which can lower the perceived temperature after wearing by 5°C. Suitable for various scenes such as sports, outdoor activities, and the office. Easy to wear, wrap it around your neck and adjust it to a comfortable position. Recommended sizes: M size (neck circumference 26-34cm) 15*17cm 124g, L size (neck circumference 34-38cm) 17*19cm 135g. Measure the neck circumference horizontally under your throat with a soft measuring tape, maintaining a natural breathing state. Some people may feel it a little tight when they use it for the first time, but they will get used to it after using it for two days. Crystallization time: Approximately 1 hour in the refrigerator (2-6°C) and approximately 30 minutes in the freezer (-18°C). After taking it out of the refrigerator, wipe off any excess moisture from the surface before use. If a refrigerator is not available, try cooling it with running water. If placed other than vertically, dents may appear on the surface after freezing, but this is a normal phenomenon of PCM crystallization and will gradually return to normal after use. Cooling duration: There is a cooling sensation of around 10°C for about 10-30 minutes after taking it out of the refrigerator, followed by a cooling sensation of 20-28°C, which lasts until the PCM inner core is completely liquid. If you feel the cooling sensation is weak, you can enhance the cooling sensation by gently kneading the product to distribute the PCM inner core evenly. Depending on the usage environment, the effect can last up to 5 hours.