The thermal conductivity (TC) of different polymeric materials is measured via four commercially available testing devices: TPS2500S by Hot Disk (Hot Disk), Transient Hot Bridge (THB) by Linseis, the Laser Flash Analysis (LFA) by NETZSCH, and the DTC‐300 by TA Instruments. The investigated materials include high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE) which are analyzed as received and after being compounded with copper particles. The filler geometry and ratio are varied systematically. Major differences in the TC generated by the different measurement methods are revealed and analyzed in detail. Moreover, material‐induced impacts on the TC as well as technology‐induced impacts on the TC are outlined comprehensively.