My mother made "corn bags" to warm our feet in bed when sleeping in an unheated room. She bought the corn in a farm supply store as she lived on the farm. I made "rice bags" for the same purpose from 1/2 of a hand towel. I just sewed up the seam, added the rice, and sewed across the top. When it gets dirty, just make another one. The rice goes to one spot but that helps it stay warm longer.