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Crosslinked polyethylene (XLPE) insulated cables are used widely for the transmission and distribution of electrical power. Although XLPE has many desirable characteristics, the addition of other polymers constitutes one way in which properties can be modified to suit particular applications. This paper describes a modified permanganic etching technique that has been optimized to permit the study of such systems by transmission electron microscopy. The approach is then applied to a range of triple-extruded (semicon/insulation/semicon) XLPE-based cables that exhibit both one and two-phase microstructures. The morphologies seen are described and the origin of preferential lamellar growth perpendicular to the semicon/insulation interface is explored. It is also shown that the apparent presence of carbon black particles well away from the dielectric interface is an artifact associated with sample preparation.