Fold the material in half with right sides together. Start at one of the short sides and sew the long side and part of the opposite short side, leaving a gap of several inches on the last short side. This is where you're going to put the uncooked rice in.
Turn the fabric tube inside out so that the rough ends are hidden.
Fill the tube with rice until it is about 2/3 full. You can also add some lavender buds or a few drops of essential oils for a relaxing experience.
Fold the remaining side in so that the rough ends are hidden and sew closed.
Notes
To use: Heat on high in the microwave for 60 seconds or until the desired temperature is reached. The exact time will depend on your microwave.