Existing test standards for ceramic insulators have not shown good correlation with actual service experience when applied to composite materials. In particular, it has proven very difficult to develop test conditions that accurately duplicate material degradation which occurs during long-term service.

The refinement of test apparatus and procedures specifically for polymeric materials remains an area of focus for a number of utilities, universities and research organizations. The Electric Power Research Institute (EPRI) High Voltage Transmission Research Center in the U.S. has developed a fog chamber that allows testing with variable levels of contamination. A specific insulator design can be subjected to a number of stresses that closely simulate the environment in which it may be used. Results of the centers aging studies indicate that the performance of silicone rubber insulators, regardless of manufacturer, is less affected by the aging conditions than ethylene propylene rubber designs. Further, silicone rubber insulators have been found to better resist contamination.

A nine-year study conducted at Chalmers University of Technology in Sweden compared the effectiveness of molded composite insulators to porcelain and glass, finding that "... the silicone rubber insulator had very low current pulses in the range of 6 mA under severe weather conditions, while all EPDM insulators showed very high discharge activity" . Utilities have been conducting field service testing on non-ceramic insulators for a number of years, and overall satisfaction has been high. Some of these insulators have been in service as long as 20 years. For example, Florida Power and Light experience with silicone has been so positive that the utility replaced many of its porcelain insulators with silicone units following the extensive damage from Hurricane Andrew. These replacements have not experienced any service interruptions from the salt contamination which plagued ceramic units, and have not displayed any of the UV deterioration found in other polymers.

Despite the advances in testing, much of the industry still relies on procedures developed decades ago for porcelain insulators. While many manufacturers have adopted specific techniques to evaluate polymer compounds, they vary from one company to another. The wide range of process conditions among fabricators also complicates the development of standard compounds for molding HV insulators. As a result, some silicone suppliers have opted for a custom formulation approach.

Current test data indicate that highly-filled elastomers offer the best electrical protection, and silicone suppliers generally try to retain as high a level of filler loading as possible and still achieve good processing characteristics. However, if a utility or insulator manufacturer insists on passing conventional tracking wheel tests or other standards that do not allow recovery time between stress incidents, it forces the compounder to reduce the level of alumina trihydrate filler.