- Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. - In metallic conductors, electrical conduction is primarily due to the movement of free electrons. - As temperature increases, the atoms within the conductor vibrate more vigorously around their lattice positions. These increased vibrations make it more likely for the free electrons to collide with the vibrating atoms, scattering the electrons and impeding their flow. - This increased scattering leads to a higher resistance and thus higher resistivity at higher temperatures.