This paper provides reliable dielectric property information on two refrigerant mixtures regarded as replacements for chorodifluoromethane (CAS no. 75-45-6) (HCFC22) and R502 (CHClF2 + CClF2CF3) (w(1) = 0.49; W-2 = 0.51). Liquid phase relative permittivity measurements are reported for R408A (CHF2CF3 + CF3CH3 + CHClF2) (w(1) = 0.07; W-2= 0.46; W-3= 0.47) and R409A (CHClF2 + CHClFCH3 + CClF2CH3) (w(1) = 0.60; W-2 = 0.25; W-3 = 0.15). The measurements were performed by using a direct capacitance method at temperatures from T = (233 to 303) K under pressures up to 16 MPa. A complete set of tables of experimental data, covering dielectric property needs for most engineering applications, is provided. The data obtained was correlated as a function of density, pressure, and temperature. The apparent dipole moments (mu*) of R408A and R409A in the liquid state were obtained from the Kirkwood modification of the Onsager equation for the variation to the modified molar polarization with temperature and density. The mu* value found for R408A was 1.043.10(-29) C.m and 1.047.10(-29) C.m for R409A. The coefficient of thermal expansion and the coefficient of compressibility in the liquid state were derived from the experimental data, with uncertainties better than 2% and 0.3%, respectively.