This IEC Technical Report presents the important material properties for polymeric materials used in outdoor insulation and, where applicable, lists the standardized test methods including the minimum requirements. If no standardized tests are available, then test methods reported in literature are summarized. This report is valid for insulating materials used in outdoor high voltage electrical applications with a system voltage greater than 1000 V a.c. having polymeric insulation including also such applications where the housing is an integral part of the devices e.g. in surge arrestors and cable terminations. The scope of this report is limited to the materials only. The performance of insulators in service depends on several factors such as the type of material, the design, environmental conditions etc. Consequently, the choice of materials that fulfil the requirements listed below is a necessary condition but does not guarantee satisfactory performance when used in outdoor insulation.