The structure and topography of surface tracking patterns generated on the surface of unfilled and filled samples of polyester resin using the international standard procedure (IEC 587, Inclined-plane Tracking Test) have been studied. The effect of contaminant now rate, applied voltage and the percentage content of particulate zinc oxide on tracking behavior has been determined. Three alternative mathematical algorithms have been used to establish the fractal dimensions of the tracking patterns as a function of the above three parameters, To model the surface hacking patterns, two methods have been applied. Firstly, a resistive network has been used in which the insulator surface is assumed to consist of imaginary vertically and horizontally placed resistors. This model is capable of producing several types of trees observed in insulating materials. However, the surface tracking patterns are mostly unbranched and it is not possible to produce realistic images with this model. The second method, Brownian motion, is mainly a recursive technique and does not take Laplacian field values into account. The resolution of the images is high, hence the simulated patterns are almost indistinguishable from the real images.