I’ve made my own for most of my running hats. I wish I could monetize it, but I can’t make a decent hat myself and don’t want to pay someone in China to make them and have to buy 1000.I took an old camping towel, (Think Shamwow) and cut it roughly 3" x 5" to fit inside the hat and sewed it down on three sides leaving the brim side unsewn. It works like a champ and the towel stays damp long after the ice melts.