When learning about the gel in baby diapers, I made a connection that it was the exact same substance used in some of the "Gel-Ice" packs we had around the house. In this video I tried demonstrating how to make a simple "Gel-Ice" at home with simple materials. It's possible that a little isopropyl alcohol could be added to help lower the temperature of the pack even more, and perhaps keep it in gel form, but I haven't experimented to find out whether or not that really works.