Montmorillonite clay is a promising filler for nanocomposite applications as it consists of sheets of atoms which can, under certain conditions, be easily dispersed. After suitable chemical modification, they can be mixed into molten polyethylene by simple extrusion. The resulting material will then have a massive internal surface area; its electrical properties may be very different to a comparable system containing only traditional micron-sized particles. The purpose of this work is twofold: Fundamental studies into the thermal, morphological and X-ray scattering behaviour are being performed with a view to gaining some understanding of the nature of the polyethylene-clay interfaces. To complement this, the electrical and mechanical breakdown strengths and molecular relaxation phenomena are being studied. It is hoped that that with a comprehensive understanding of the behaviour of these systems, it might be possible to tailor their physical properties to particular applications.