The national utility (Originally Eskom), had undertaken comprehensive evaluation of coating materials over a number of years at their Koeberg Insulator Pollution Testing Station. Situated on the west coast of the South Africa, the various energized samples are exposed to the extreme marine conditions characteristic of the site. Physical degradation, leakage current amplitudes and flashover occurrence are closely monitored. As an example of the results achieved at this facility, Figure 1 shows the relative cumulative leakage current flow on three identical insulators – two of which are coated with different brands of silicone rubber and the third left un-coated. It is evident that the silicone rubber significantly improves the insulator performance and, further, that the extent of the improvement is dependent on the type of rubber used.