Cold plasma technology represents a promising approach to reduce the chemical emissions of wastewater treatment using partial discharges for the degradation of chemical substances. However, the wet environment in the plasma generator coupled with the chemical stress due to high ozone concentration results in erosive effects on the utilized insulation materials, ultimately leading to their preliminary failure. The time-dependent erosion of wet polymeric insulation materials was investigated under repetitive voltage pulses by measuring the eroded volume of the following polymers: polyamide 6.6, polyvinylchloride and polytetrafluoroethylene. Additionally, microscopic images of the polymer surface were taken to examine the underlying degradation processes. The investigations show that the erosion resistance of the polymers against partial discharges is dependent on the material. The degradation process is influenced by various factors, including water absorption and thermal resistance.