As early as the 1980s, the US military was beginning to see
aircraft fires and crashes related to electrical short circuits.
Studies showed that Kapton was far from the ideal insulator
everyone had hoped it would be — it tended to develop
circumferential cracks from the slightest of nicks, exposing the
conductors within. Kapton is also easily degraded by moisture,
exacerbating the problem in humid environments or areas of an
aircraft subject to moisture, like galleys and lavatories.
Once the insulation is compromised, arcing can occur, which leads to charring of the Kapton. This changes the insulation’s dielectric properties, turning it into a conductor. In some cases, this led to overloaded circuits that were not detected by circuit breakers, since the insulation was carrying the excess current rather than the conductor. Other times, the circuit breaker would trip to protect the circuit, but when the crew reset the breaker, the charred insulation would catch fire and burn like a fuse, flames traveling along the wires far from the original arc...
(C) https://hackaday.com/2018/04/04/kapton-miracle-material-with-a-tragic-history/