Posted about this last August and it bears repeating. The neckband currently chilling in my fridge is a cotton tube filled with medium-size polymer. You soak it in ice water for 20+ minutes, blot, and tie around your neck. Resoak and reuse as necessary. You can buy the polymer
online and you can also use the crystal stuff that you use to hydrate plants (thanks
wendy_lady!) These really do work. Stay cool everyone!