The topic of the fire retardancy of cable compounds has been gaining a great interest, nowadays. Unfortunately, it is due to the fact, that the safety in the event of fire has gradually decreased in the last few decades. Therefore, tightening of the fire retardancy requirements by introduction of a new Construction Products Regulation this year was a necessary step for ensuring the safety of newly constructed buildings within the EU. This situation has led to the new technological challenges, which in some aspects have not been fully solved. One of these challenges are the development of economically acceptable cable halogen-free polymer compounds with the high level of fire retardancy, long service life and wide processing window, which is from the customer side a highly expected. Therefore, the motivation of this article is to provide an investigation of mechanical and thermal responses of HM4 thermoplastic HFFR compounds of the 3rd generation – filled by Halloysite nanotubes (HNT) and Spherical nano amorphous SiO2 (SA-SiO2). Presented compounds were designed as a sheeting, suitable for 1kV applications with the operational temperature up to 90°C, fulfilling the requirements of VDE 0276-622, IEC 60502-1. Base formulations are consisted from: EVA, LLDPE, ATH (>60%), compatibilizers, HNT, SA-SiO2 and AOXs and were prepared on laboratory twin-extruder Leistritz. Results show a significant reduction of the heat release rate exceeding 40 % in comparison with the reference compound measured by Cone Calorimetry, improved char forming and increased LOI after the incorporation of 3% HNT into the formulation. Also, a strong synergism between HNT and SA-SiO2 has been observed in tested compounds in terms of self-extinguishing behaviour, peak heat release rate reduction, as well as, an improved mechanical properties. The reason for these phenomena can be explained by improved dispersion of all nanoparticles provided by SA-SiO2, which act as a ball bearings during the extrusion.