The effect of fluorine incorporation on dielectric properties has been studied for a series of polyimides in order to distinguish between several contributing mechanisms to the generally observed decrease in the relative permittivity. Using low-frequency capacitance measurements after exhaustive in situ drying, in conjunction with refractive index measurements, the overall decrease in dielectric constant was semiquantitatively assigned between changes in the three modes of polarization via the use of fluorine/hydrogen and symmetric/unsymmetric analogs. These results suggest that replacement of hydrogen with fluorine always lowers the dielectric constant increment due to the electronic mode of polarization, has little effect on the atomic increment, and in the case of asymmetric fluorine substitution, results in an increase in the orientation increment. Values for each of these effects are reported.