Got some more from Wikipedia:

According to a NASA internal report, space shuttle “wires were coated with an insulator known as Kapton that tended to break down over time, causing short circuits and, potentially, fires.” The NASA Jet Propulsion Laboratory has considered Kapton as a good plastic support for solar sails because of its long duration in the space environment.

Kapton is also commonly used as a material for windows of all kinds at X-ray sources (synchrotron beam-lines and X-ray tubes) and X-ray detectors. Its high mechanical and thermal stability as well as its high transmittance to X-rays make it the preferred material. It is also relatively insensitive to radiation damage. Another prominent material for these purposes is beryllium.

The thermal conductivity of Kapton in temperatures from 0.5 to 5 kelvin is rather high κ = 4.638×10−3 T0.5678 W·m−1·K−1. This, together with its good dielectric qualities and its availability as thin sheets have made it a favorite material in cryogenics. Kapton is regularly used as an insulator in ultra-high vacuum environments due to its low outgassing rate.

So on the one hand Wikipedia states it has great mechanical properties, on the other hand it breaks down over time.