Climate change is pushing the electrical engineering community to replace sulfur hexafluoride, the most potent greenhouse gas currently used in high- and medium-voltage insulation systems. In this context, hybrid insulation systems—combining a solid dielectric, typically a polymer, with an environmentally friendly gas—represent a promising alternative. However, ensuring their reliability requires a deep understanding of charge accumulation phenomena at gas/solid interfaces, which strongly influence the initiation of electrical discharges. This thesis investigates surface charge dynamics in polymeric materials (PP, PVC, PVDF, PTFE) through surface potential decay (SPD) measurements. The decay curves were analyzed to estimate the trap density within the dielectrics and fitted using a bi-exponential model to extrapolate the potential evolution over extended time periods.