HV transformer isolation

[The Electrician]

Thanks for that, I didn't realize, even big suppliers like RS use polyamide when referring to Kapton 

I have bought that fake Kapton and I will test a few layers of it with 20kV before using it in my transformer.

I'm also investigating these polyester tapes, they are very affordable compared to genuine DuPont Kapton, and they seem good according to the datasheet

These guys have what you need: https://www.ibselectronics.com/permacel/

Including Kapton tape: http://www.ibselectronics.com/ibsstore/catalogsearch/result/index/?searchKind=http%3A%2F%2Fwww.ibselectronics.com%2Fibsstore%2Fcatalogsearch%2Fresult%2Findex%2F&s=p-222&q=p-222

Also, Nomex is good stuff: https://www.eis-inc.com/paper-type-roll/p-ph21-nomex%20410-rl

[Neukyhm]

Well the fake Kapton tape is still on its way. I have bought polyester tape as well: https://docs-emea.rs-online.com/webdocs/1439/0900766b81439724.pdf

It's a 3M T1350, with a 5.5kV breakdown voltage. However, there is another tape, T56 from 3M, that is designed for layer insulation according to the datasheet, but it has 5kV breakdown voltage (less that T1350). Also it's more expensive.

You will probably say that there is no reason to be concerned because both tapes will do the work and you are right, it's just that I don't want to kill another transformer xD 

T1350 should be fine, the main difference is that this tape's adhesive is acrylic and T56's is rubber, I don't know what's best to stick to full cured epoxy.

This tape thing is an entire new and huge world dude.