The quartz crystal microbalance/heat conduction calorimeter (QCM/HCC) is a versatile instrument coupling both gravimetric and calorimetric techniques. The QCM/HCC is used to probe vapor sorption in thin films. Three parameters are measured simultaneously as a thin film undergoes vapor sorption, namely: mass changes in the film (+/- 10 ng), corresponding thermal effects upon vapor sorption (+/- 100 nW), and motional resistance (+/-0.5Omega) changes within the film. A range of film thicknesses (0.75 to 8.5 mum) of the polymer, Tecoflex(TM) are cast on QCMs and the interaction of each film with ethanol and water is determined. From the direct calorimetric measurements, sorption enthalpies (A(sorption)H kJ/mol) are determined for the film-vapor interactions. Sorption isotherms are then analyzed for each film. The isotherms shown here generally display a linear Henry's Law dissolution relationship between the vapor pressure and the amount of vapor sorbed into the film. Motional resistance data provides a window to view viscoelastic effects of the polymer films upon vapor sorption. Motional resistance data are compared for ethanol sorption in a relatively thin (0.75 mum) and thicker (8.5 mum) Tecoflex(TM) film. (C) 2004 Wiley Periodicals, Inc.