Geothermal heat pumps are widely used as an eco-friendly and cost-effective house heating/cooling system. Crosslinked polyethylene (PEX) materials have been successfully used in domestic hot and cold water piping due to their good properties such as high-temperature strength, good elastic modulus and high impact resistance. It is well known that the addition of carbon filler materials in a polymeric matrix leads to higher thermal and electrical conductivity and improved mechanical properties. In this work, PEX composites containing a commercial type of graphitic filler with a mean particle size of 15 ìm that exhibits optimized conductivity properties were prepared and studied. The filler content was 0.5, 1, 2.5 and 5 wt%. A silane crosslinking catalyst was incorporated in PEX during the melt compounding process and the final composites were crosslinked in a water bath at 90 °C for 24 h. Thermal, mechanical and thermal conductivity properties of the composites were evaluated and it was found that Young’s modulus increases when increasing the filler content, thermal stability remains unaffected, and thermal conductivity increases up to ~35% with 5 wt% graphite in comparison with neat PEX. In conclusion, PEX/graphite composites are promising materials for geothermal piping systems with improved properties. ACKNOWLEDGEMENTS: Ôhe authors wish to acknowledge co-funding of this research by European Union-European Regional Development Fund and Greek Ministry of Education, Research and Religions/EYDE-ETAK through program EPANEK 2014-2020/Action “EREVNO-DIMIOURGO-KAINOTOMO” (project Ô1ÅÄÊ-02611).