Under one aspect, a method of cooling a circuit element includes providing a thermal reservoir having a temperature lower than an operating temperature of the circuit element; and providing a nanotube article in thermal contact with the circuit element and with the reservoir, the nanotube article including a non-woven fabric of nanotubes in contact with other nanotubes to define a plurality of thermal pathways along the article, the nanotube article having a nanotube density and a shape selected such that the nanotube article is capable of transferring heat from the circuit element to the thermal reservoir.