Abstract: The present invention provides for an insulating boot 20 for ends of through-bolts 12 in electric generators that comprises a shaped insulating boot. The boot has an inner surface and an outer surface and an opening, where the inner surface is substantially free of protrusions. The inner surface of the shaped boot 20 is within 0.01 to 0.5 inches (0.025–1.3 cm) larger than the shape of the end of a through-bolt 12 to which the shaped boot will be applied. The shaped insulating boot has a breakdown voltage of at least 10 kV, and more particularly at least 30 kV, and the shaped boot is placed over the end of a through-bolt of an electric generator.