Flexible and conductive polyolefin–rubber composites were formed by melt mixing polyethylene and reclaimed rubber through interactions of pre-functionalized polymers in interface. Composite of varying compositions were formed via selective localisation of carbon nanotubes in polyethylene phase. Composites were extruded to form filaments to be used for fused deposition modelling (3D printing), which is an additive manufacturing process. Composite test samples were built layer by layer via Makerbot Replicator 2X. Effect of carbon nanotubes on the thermal, mechanical properties and the electrical conductivity of the resultant composites were assessed. Enhancement of electrical conductivity was explained by changing phase morphology of the polyethylene–rubber composites.