Resistance is additive when several conducting layers lie between the hot and cool regions, because A and Q are the same for all layers. In a multilayer partition, the total conductance is related to the conductance of its layers by: R = R 1 + R 2 + R 3 + ⋯ ⋯ or equivalently 1 U = 1 U 1 + 1 U 2 + 1 U 3 + ⋯ ⋯