► Polycarbonate polyurethane films modified with expanded graphite (EG). ► Thermal and dynamical thermal analysis indicates changes upon addition of EG. ► Relaxation processes and conductive phenomena (MWS and EP) are discussed and related with the EG content. Segmented polycarbonatediol polyurethane (PUPH) has been synthesized and modified with different amounts of graphite conductive filler (from 0 to 50wt%). Thermal and dynamical thermal analysis of the composites clearly indicates changes in the polyurethane relaxations upon addition of graphite. Broadband dielectric spectroscopy has been used to study the dielectric properties of the (PUPH) and one composite in the frequency range from 10−2 to 107Hz and in the temperature window of −140 to 170°C. Relaxation processes associated with different molecular motions and conductivity phenomena (Maxwell–Wagner–Sillars and electrode polarization) are discussed and related to the graphite content.