Aluminium films were r.f. sputtered onto vycor slides. Annealing induces a decrease of resistivity at temperatures between 300 K and 414 K. Isothermal resistance recovery occurs with a constant rate depending on the annealing temperature; the activation energy increases from 0.3 eV to 0.4 eV for increasing thickness. The resistivity recovery is attributed to a surface reordering phenomenon, which is in good agreement with the Mayadas–Shatzkes conduction occuring in these polycrystalline films, with a thickness independent mean grain diameter. Reflections on grain boundaries are independent of ageing, whereas the reflection coefficient on the upper surface is increased.