Abstract: A portable heating device includes an envelope made by heat-sealing the edges of two flexible polymeric films, and a heat source within the envelope including, in one embodiment, a ribbon of conductive resistance heating element material folded into a generally sinuous, flat pattern within the envelope, and a nonconductive liquid such as silicone oil in the envelope and surrounding the heating element. In a second embodiment, the heat source is a semiconductor device. The envelope is carried by a strap or the like to hold the envelope next to a selected portion of the body for localized heating thereof. The heating element in the first embodiment is electrically connected to a power source such as batteries, and, in the second embodiment, the semiconductor device is connected to a control circuit which is connected to batteries.