cap types in a bias t for 100watts power tx hf

[p.larner]

can metalized 4kv Metallized Polyester Capacitor types be used in this type of bias t?.

[coppercone2]

what is the ESR of the capacitor at the frequency of interest. then you can figure out how hot it will get. then you can figure out if the life time is effected

[TimFox]

For what frequency range?
Polyester does not have very high Q over its useful range compared with polypropylene or polystyrene, so will have some loss.
Also, film capacitors can easily have self-resonant modes (series resonance) in the MHz region, so will look inductive at higher frequencies.
I used to use ceramic or porcelain capacitors in this shape, with broad ribbon leads, for high-power RF circuits, but they seem to be hard to find now:
https://exxelia.com/en/product/detail/464/spt519-caw-cew-series

[p.larner]

mostly hf 160-10m

[TimFox]

The polyester capacitors will not work well at 30 MHz (10 m).