This article presents a perspective overview on the functional properties of polymer composites based on multi-walled carbon nanotubes (MWCNs) followed by novel data on the integration of nanoparticle cobalt oxide with enhanced mechanical and thermal stability. Introducing MWCNTs into a polymer matrix leads to the formation of nanocomposites with enhanced reinforcement, thermo-photo oxidative stability, fire resistance and heat-transfer capacity. The performance of the nanotubes is prevalent regardless of the type and nature of polymers. The nanocomposites can withstand the onset of various aggressive agents due to their ability to terminate destructive free radicals in the MWCNT framework and the formation of a protective carbon film on the polymer surface associated with its uniform distribution. A novel study on the effect of MWCNTs on the properties of composites based on high-pressure polyethylene (HPPE) modified with cobalt oxide nanoparticles (NPCoO) is presented here. Improvement is shown in the strength and deformation parameters, as well as in the thermal-oxidative stability of the obtained nanocomposites. These enhanced properties can be attributed to the effects of structural and chemical stabilization of the polymer matrix by the enhanced radical scavenging and trapping properties of the MWCNs. Small amounts of the NPCoO nanofillers when introduced into the polymer also play the key role as structure-forming agents to create artificial nuclei for crystallization. This effect contributes to the formation of small spherulite structures in the nanocomposites imparting improved physical, mechanical and thermal properties.