The aim of this work was to modify the surface of a nucleating agent in such a way that both the foaming process and the crosslinking of polyethylene are supported. The first part of the work consisted of binding two types of initiators to the surface of the nucleating agent. These initiators do not only release gas to support the foaming process, but also form stable radicals to support silane crosslinking. With the help of various analytical methods, it could be demonstrated that the initiators can be bound to the surface of the nucleating agent. Moreover, the influence of the modified filler on the crosslinking reaction was investigated. For this purpose, crosslinked samples were produced both on a laboratory scale and by reactive extrusion. The influence of the molecular structure of two polyethylene types on crosslinking was also investigated. The gel content, swelling ratio, crosslink density, and molar mass between adjacent crosslinking sites (Mc) were measured. These results indicate that the formed radicals of the thermal initiator linked to the talcum supported the crosslinking process and led to a better crosslinking network.Both methods, in laboratory scale and by reactive extrusion, showed that the use of the modified filler led to a higher crosslinking density. In the next step, the influence of the modified talcum on the foam morphology was investigated. For this study, the polymer was physically foamed in an extrusion process with nitrogen as blowing agent and pure and the modified talcum as nucleating agent. The foamed samples with the modified talcum achieved a smaller average cell diameter and higher cell density compared to the use of the pure talcum. It seems that the additionally formed gas led to a more uniform foam structure and that the initiator linked to the talcum surface supports the foaming process. By modifying the surface of talcum with an initiator, we found a possibility to support and improve the crosslinking process and foaming process of polyethylene.