I've made hundred and sold at craft sales. Since I'm not doing it any long I'll tell you my secret. Like yours, I use rice but I also line mine with WnN and that keeps it warm even longer and cold longer too. Since these can't be put in the washing machine ( imagine the look of the machine....... ) I also made a little "pillow case" to go over it and that can be thrown into the wash. Very popular and even though I haven't done any sale for a year, people still call to have me make more.