Aim of this thesis was to optimize, in cooperation with the company Steinbacher Daemmstoffe, the thermal conductivity of a polyethylene, by addition of various fillers to improve the foaming behaviour to lower thermal conductivity. In foamed plastics the thermal conductivity depends on the cell formation which is linked with the melt strength. Higher melt strength supports the formation of small cells. The cell density has an important role. Higher cell density reduces the thermal conductivity because the heat transfer through the material is disturbed. To realize this, different nanofillers were used because they can improve especially the melt strength. Moreover, cellulose fibers were used, because they have a very positive effect on the cell density. In order to make a statement, which filler brings the maximum increase in the melt strength, individual formulations were produced. Experimental determination of the drawing force showed that the maximum increase in melt strength can be achieved with formulation Nanofil 5. The results of formulations with cellulose fiber exhibited a promising increase in the melt strength. Furthermore, significant differences between the different concentrations, in terms of the maximum melt strength, were detected for formulations with Nanofil 5 and cellulose fiber. For this purpose these two fillers were used for the further investigation. The results of the heat conductivity measurements are promising. By addition of the filler Nanofil 5 the thermal conductivity is equal compared to the matrix polymer or due to low degrees of filling no increase could be detected. Furthermore, the thermal conductivity of the formulations with cellulose fiber is above the crystallization temperature about 20 % higher than those of the unfilled polyethylene. This increase could be advantageous for processing. However in field of application these formulations are in the range of the base polymer. By addition of these fillers it is possible to improve the melt strength of the polyethylene with equal thermal conductivity. Furthermore, it could be shown that layered silicates and the cellulose fiber have improved nucleating behaviour. However, there is still a considerable potential for optimization. Consequently, it should be possible to produce foamed insulation materials with these formulations, which have a reduced thermal conductivity. Due the increased melt strength small cells should be expected in the finished product.