Insulated molecular wires formed from organic molecules may have promising applications in organic and flexible electronic devices. Here, the authors provide compelling evidence of the formation of insulated molecular wires by sheathing conducting regioregular poly(3-butylthiophene-2,5-diyl) (P3BT) fibrils with insulating nanotubes from 3,5-bis-(5-hexylcarbamoylpentyloxy)-benzoic acid decyl ester molecules through a nucleation and growth process. For dilute systems, conducting atomic force microscopy together with force-distance curves and current-voltage spectroscopy are concomitantly performed to sense current from the topmost surface to the core of the composite fibrils at controlled tip indentation depths. Results show that current is sensed only when the core of the nanocomposite fibrils is reached which indicates the presence of an insulating layer around the semiconducting P3BT fibrils. The existence of this molecular nanocomposite is further supported by neutron scattering experiments carried out on more concentrated systems at different temperatures.