Corrosion of B films in air can limit their practical applications. Here, we study the evolution of the elemental composition, thickness, and morphology of 10-100-nm-thick amorphous B films sputter-deposited onto glassy carbon substrates and stored under different conditions. Results show that films with thicknesses of greater than or similar to 55 nm have expected excellent corrosion resistance during storage in laboratory air at room temperature over several months. In contrast, less than or similar to 45-nm-thick films exhibit pronounced degradation upon air exposure, starting with a change in the composition to similar to 30 and similar to 50 at.% of O and H, respectively. After such an O and H uptake, the degradation proceeds via mass loss with a characteristic time constant of similar to 5 days in air at room temperature. A post-deposition annealing at 1000 degrees C in an inert atmosphere makes all the films corrosion resistant. (C) 2018 Elsevier B.V. All rights reserved.