1. Use PCM frozen at 64 degrees Fahrenheit (10 minutes in ice water, 20 minutes in refrigerator) 2. There's no condensation, so your neck and clothes won't get wet. 3. Use non-toxic TPU fabric. Tight seal, durable, long service time, not easy to tear, not easy to damage. 4. The technology was developed and researched to protect astronauts from sudden changes in temperature. 5.PCM materials freeze faster and longer than water or other liquids.