Measurements of the electrical resistivity at 296°and 4.2°K in aluminum films, evaporated both in an ion-pumped ultrahigh-vacuum system and in conventional oil-pumped systems onto unheated glass substrates, are presented and used to calculate the intrinsic mean free path and intrinsic electrical resistivity at 4.2°K. It is shown that the UHV films are characterized by a maximum mean free path of the order of 1 μ and by smaller residual resistances than other films. While the mean free path so obtained is still several orders of magnitude smaller than the published value for high-purity foils of bulk aluminum, it is nevertheless not small enough to appreciably influence the resistivity at 296°K which is measured to be ≈60% higher than the bulk value. This discrepancy, which may be due to structural effects, emphasizes the view that the sample artifact of adding the bulk thermal resistivity to a residual resistivity can be misleading in the case of thin films, even when surface scattering is accounted for. © 1968 The American Institute of Physics.