The dynamic glass transition and the dilatometric glass transition temperature are simultaneously characterized in thin films of hyperbranched aromatic polyesters by broadband dielectric spectroscopy and capacitive scanning dilatometry. A diverging thickness dependence is detected: while the temperature position of the alpha relaxation peak T-alpha decreases by similar to 30 K, the dilatometric T-g increases by similar to 10 K with decreasing film thickness. This emphasizes the subtle character of the glass transition phenomenon-as manifested in the molecular dynamics and in the (structural) thermal expansion-and proves that, in contrast to the bulk, different experimental techniques do not necessarily deliver similar results in confinement. (c) 2006 Wiley Periodicals, Inc.