A thermal switch selectively couples a heat source to a pair of heat sinks. The thermal switch includes a shunt that is thermally coupled to the heat source. The shunt has a pair of posts. End portions of the posts are at least partially radially surrounded by respective cups. The cups in turn are thermally coupled to respective of the heat sinks. The cups are made of a material with a larger coefficient of thermal expansion than the material of the posts. Activation of one of the heat sinks causes the cup corresponding to that heat sink to contract, bringing it into contact with the corresponding post of the shunt. This opens a heat path through the switch from the heat source to the activated heat sink. Thermal isolation of the second cup is facilitated by an axial isolator of high thermal impedance, facilitating isolation of the inactive heat sink.