Efforts to optimize the use of silicon rubber and epoxy resin as an insulating material in the electricity sector continues to be done where one of them is looking for filler are cheap and easily obtained. So in this paper is described about the use of coal fly ash as filler for silicone rubber and epoxy resin, where it is known that fly ash has a very fine particle size that is potentially as filler. Utilization of coal fly ash as filler will help solve problems in the field of environment in Indonesia because these materials as a hazardous waste. So as to determine whether the fly ash can improve the performance of silicone rubber and epoxy resin, it has carried out research on the performance characteristics of silicone rubber and epoxy resin that are conditioned on the wet environments that were simulated by immersion in water for 21 days. Parameter measurement that has been observed is the contact angle, the weight of the test material, and the relative permittivity. The results obtained are fly ash allowed to function as a filler in silicone rubber in wet environments due to the difference in the average value of measurement results between silicone rubber without filler (SRFA0) with silicone rubber which has a filler (SRFA30) ie for a contact angle of 1.3, weight gain 0.2%, and the relative permittivity of 1.4. While on epoxy resins, fly ash is less possible is used as filler in wet environments, because difference between the average value of the measurement results between the epoxy resin without filler (EPFA0) with epoxy resins which has a filler (EPFA30) ie to the contact angle of 4.7, the weight gain of 4.6%, and the relative permittivity of 4.8.