The molecular dynamics in thin polymer layers having a free upper interface is investigated by means of Broadband Dielectric Spectroscopy and AC-calorimetry. Down to film thicknesses of similar to 10 nm no shifts in the average relaxation time and no broadening of the dynamic glass transition are detected for polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(gamma-benzyl-L-glutamate) and poly(2-vinyl pyridine). This experimental finding restricts to a few nanometers the length-scale of a possible alteration of the polymer mobility in the vicinity of free interfaces.