My sis was given a whole set made with old t-shirts, but they were filled with untreated "deer corn"... I'm a town-girl, married to a town-boy, so I'm not exactly certain what "deer corn" is, but I think it's what hunters buy to put in their deer stands? She shared with me on a trip once and they are wonderful!! When we'd stop for fuel, we'd heat them up in the store's microwave... wonderful for stiff necks, hips, knees, whatever!! She also uses them to warm her toes when she goes to bed... oh yeah...