Abstract The long-term exposure of the cable insulation, which are very often manufactured from polymers, to the standard operational environment conditions in nuclear power plant (NPP), such as radiation, heat and humidity, can cause ageing and degradation of their functional properties. Polymers exposed to such factors as ionizing and gamma radiation, undergo significant structural and functional modifications. In order to simulate NPP conditions, one can perform ion irradiation with different irradiation fluences to test insulation of the materials and determine their resistance to radiation. It is known that the main effect of radiation is hydrogen release from polymer. This phenomenon leads to the increase of hardness, shrinkage of the material and deterioration of material resistivity. Polymer materials exposed to ionizing radiation become fragile, stiff, prone to fracture and breaking. In the case of cable insulation, one of the most significant problem is the decrease of their electrical resistance. In this study, structural properties of pristine and irradiated polymer insulation were assessed by Scanning Electron Microscopy (SEM), Raman spectroscopy and resistance measurements. The phase composition was identified by Raman spectroscopy technique. It has been found out that these properties are strongly related to the ion irradiation and structure of the material. Reported findings points to the observation that current-voltage (I-V) characteristics depend from ion irradiation fluence – and material resistivity gradually decreases with the increasing fluence of ions.