XLPE or Cross-linked polyethylene is a thermoset insulation material. Crosslinking polymers is a process which changes the molecular structure of the polymer chains so that they are more tightly bound together and this crosslinking is done either by chemical means or physical means. Chemical crosslinking involves the addition of chemicals or initiators such as silane or peroxide to generate free radicals which form the crosslinking. Physical crosslinking involves subjecting the polymer to a high energy source such as high-energy electron or microwave radiation.
Polyethylene (PE) material itself has excellent dielectric strength, high insulation resistance, and a low dissipation factor at all frequencies making it an ideal insulator, however it is limited in its temperature range. Cross-linking the PE to become XLPE increases the temperature range of the insulation whilst maintaining the electrical properties.