The disclosure provides a process for producing a material with improved breakdown strength. The process includes heating a polymeric composition composed of a low density polyethylene (LDPE) and a minority amount of a high density polyethylene (HDPE). The polymeric composition is heated to at least the melting temperature of the HDPE. The process includes control-cooling the heated polymeric composition at a cooling rate from 0.1° C./min to 20° C./min, and forming a polymeric composition. The control-cooled polymeric composition has a unique morphology which improves breakdown strength. Also provided is a coated conductor with an insulating layer composed of the polymeric composition with the unique morphology. The insulating layer exhibits improved breakdown strength.