Natural heating pads. I just made one of these for my husband (who has a bad back). Stitch a rectangle and stuff with rice, corn, or dried beans. Microwave for 30 seconds to 3 minutes (depending on size). Use. It's that simple, and I had a lot of beans that were too old to use for anything else. You can also add a few drops of essential oil to the filling before you stuff the sack.