We present results for physical aging of films made from a high free volume polymer (poly-[1-(trimethylsilyl)-1-propyne], PTMSP). Aging was tracked by gas permeation measurements of He and Nz. The intermediate and thin films (3 and 1 mu m) showed a rapid loss of gas permeability with time while the thick film (85 mu m) showed no significant permeability change over more than 200 h. The permeability loss accelerated with decreasing thickness. The films were carefully conditioned to imprint a reproducible history. We conclude that bulk PTMSP apparently exhibits stable permanent gas permeabilities, but thin films appear prone to accelerated physical aging. This complements our earlier observations on a number of polymers. The results further support the hypothesis that free volume from the glassy material is eliminated over time at the surface of the films in a diffusion-like process.