Writing
where  is the conductance, in W/(m K).
Fourier's law can also be stated as:
The reciprocal of conductance is resistance,  is given by:
Resistance is additive when several conducting layers lie between the hot and cool regions, because  and  are the same for all layers. In a multilayer partition, the total conductance is related to the conductance of its layers by:
 or equivalently 
So, when dealing with a multilayer partition, the following formula is usually used:
For heat conduction from one fluid to another through a barrier, it is sometimes important to consider the conductance of the thin film of fluid that remains stationary next to the barrier. This thin film of fluid is difficult to quantify because its characteristics depend upon complex conditions of turbulence and viscosity—but when dealing with thin high-conductance barriers it can sometimes be quite significant.