Abstract: A dynamoelectric machine core and coil assembly characterized by having a separately insertable conformable side filler, such as resin impregnated fiber glass provided with a plurality of ridges of an electrically semi-conductive, pressure-deformable elastomer bonded to one side thereof. In the assembly the conformable side filler is compressed between the side of a coil-receiving laminated core slot and the relatively smooth sides of coil windings mounted in the slot. As thus compressed, the side filler forms a good thermally conductive path between the somewhat irregular coil sides and the core to thereby prevent undesirable temperature rises. The side fillers also prevent insulation-destroying vibration of the coils in the slots, and due to the semi-conductive nature of the side fillers, they prevent the formation of corona across any voids that might exist between the sides of the coil insulation and the sides of the coil-receiving slots.