Material: Main raw material outer layer TPU, content PCW phase change material 1. Place the collar in an environment below 28°C to cool and solidify. (Cold water or refrigerator, etc.) 2. When the content solidifies, wear it on your neck with both ends of the opening facing forward 3. After the content melts into liquid, cool and solidify the collar again and reuse it. (It is recommended to place it on the flat surface of your hand) When the ambient temperature is below 28°C, it will begin to solidify. The required cooling (solidification) time: about 30 minutes in cold water, about 15 minutes in ice water, about 20 minutes in the refrigerator, and about 10 minutes in the freezer.