The discharging behavior of Mylar polyethyleneterephthalate (PETP) films is investigated and discussed in terms of dipole relaxation at 85℃ as well as conductivity and trap dynamics at higher temperatures. For comparison, the low-temperature peak due to positive real charge in nonpolar fluoropolymer Teflon FEP is also described. The shift of the mean charge depth in PETP samples charged at elevated temperatures, the transport of detrapped real charge in the bulk of PETP, and the compensation of detrapped charge in the bulk during thermally stimulated discharge are studied by means of heat-pulse experiments as well as measurements of the steady-state conduction current and the bulk conductivity glow curve.