Oh, these work nice!  I used one recently at a VERY HOT craft show outside.

Soak in cool water for about 5 minutes.  There is a product that soaks up the water and swells up and keeps the water cool.  As you 'wear' it around your neck, you keep turning it, kind of like flipping to the cool side of your pillow.  The surrounding air and the wet material keeps the temp cool, while you keep turning it.  

During my recent use, I had to resoak since the air and my skin dried it out!  

Contact me for what I have already made or what I can make for you.