The emergence of nano dielectrics for specialized high voltage applications sparked off a variety of research activities, which proved that nano-fillers are capable of improving the electrical, thermal and mechanical properties of polymers. This paper primarily investigates the effect of addition of hBN (hexagonal boron nitride) nanoparticles into an epoxy polymer base by increasing fill-grade, from 0.2 to 5 % by volume, from two different standpoints: (a) characterizing the electrical space charge (S.C.) accumulation threshold under DC electrical fields, and, (b) demonstrating the alterations in material properties of the modified polymeric materials, from the unfilled polymer. Objective (a) is experimentally investigated by the pulsed electro-acoustic (PEA) technique, well known for determining spatial charge distribution in dielectrics. Objective (b) is investigated by determining the ultrasonic velocity response of the modified composites and unfilled polymer. The obtained results suggest a relation between electrical threshold fields for S.C. accumulation fill-grades, as well as the fact that incorporating stiff filler materials into brittle polymer bases leads to a tougher composite (capable of withstanding greater breaking stress levels), but with reduced ductility.