The present invention is directed to a self regulating heater including a first layer made of a thin and flexible electrically insulating material. A second electrically conductive layer includes first and second buses spaced from each other. A third resistive layer electrically connects the first and second buses. The third layer has a higher electrical resistance than the second layer. The third layer experiences a positive temperature coefficient (PTC) effect when heated. A fourth interface layer directly connected to at least one of the second electrically conductive layer and the third resistive layer directly engages skin of a patient when the heater is attached to the patient. A combined thickness of the first layer, the second conductive layer, the third resistive layer and the fourth layer may be between 5 mil and 20 mil.
