1 Part Rubbing Alcohol
3 Parts Water
Place in a freezer bag (i.e. ziploc freezer bag, quart or gallon works best)
Place in freezer for a few hours before use. After use, refreeze. Due to the alcohol being in the ice pack, it will remain "movable".
Not sure what 1 Part to 3 Parts is? For instance: 1 Part = 1 Cup Water to 3 Parts = 3 Cups of Water!