The polarizability parameter, pi* from the theory of Kamlet and Taft was measured for 1,1,1 3-tetrafluoroethane (HFC 134a) as a function of temperature and pressure, to cover the liquid and supercritical states. The polarizability changed with the reduced density of the fluid and three distinct density regions were observed. The relative permittivity was also measured over the range 30-130 degrees C and 40-300 bar and used to model the pi* data. The mean sphere approximation (MSA) model was applied to the data and found to produce an excellent fit to the data in both the liquid and supercritical. states. The values of pi* are also shown to have good correlation to the solubility of water in these media.