The rate of heat flow depends on the mode of heat transfer and on the temperature difference across which the heat flows, as well as on the matter of the system under consideration and its geometry.
There are three types of heat flow:
The electrons of a metallic solid conduct nearly all of the heat through the solid. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, also conducts heat well.
The Peltier Effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid.
Weatherization slows convective heat flow in buildings. Insulation slows conductive heat flow. Reflective barriers slow radiative heat flow, and often couple directly with insulation.
For more on heat transfer, see heat.