The quick progress in the development of electrical insulating materials allowed significant miniaturization of electric and electronic components. Today dielectric materials with very high performance are available. But there exists no long-term experience about the behavior of very small insulating distances (creepage distances). Especially under the influence of pollution. Because of this lack of information investigations of a large number of modern insulation materials were carried out. Small creepage distances on these materials were exposed to the influence of natural pollution. The insulating-characteristics of the polluted insulating distances were investigated under well defined climatic conditions. One essential result of these investigations is that the withstand capability of the small insulating distances is strongly influenced by the ability of insulating materials to adsorb water on the surface. This ability is the most important parameter for the insulation characteristics of small insulation distances.
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