AbstractInvestigations are reported on high‐ and low‐temperature vulcanized silicone rubber composite insulators that were exposed to service for three, nine and eleven years under industrial or marine pollution conditions. Wetting angles and thermally stimulated depolarization (TSD) current spectra were measured. Microscopic observations of selected insulator surfaces were carried out as well. The prolonged services cause gradual and inhomogeneous losses of hydrophobicity on surfaces and inside of insulator housing materials. It is shown that there exists a correlation between the measured TSD current spectra and the wettability changes. In addition, the spectra also allow to predict an ability to support a process of hydrophobicity recovery at a housing surface. It seems that TSD measurements may be applied as a complementary test method during performance assessment of silicone rubber composite insulators.