It is called Watersorb. You can goggle and find a site to
order it on line. A 4 lb pkg is about $34 with free shipping.
You only use 1 1/2 teaspoons per neck cooler so goes a long ways. After using let it dry thoroughly and the
crystals dry down to nothing again and you can use it next
season. These are great for anyone working outside in this
heat. I buy the big bag and share it with friends.