Hi guys:
This is something I've made for myself and it works quite well so I took it to Tindie.
I hope the admin will permit me to post this here.
It basically beats the best out there due to the 0.5mil dimension thickness which allows a 0.1°C-in²/W thermal impedance when thermal paste is used.The caveat is lower voltage (<200V tested) apps. Its material specs look to be better than double that though, but I haven't had to use it in that range.
For us home brew folks, cheaper & better is always a good thing. So if you use To220,To3 or To247 devices as I do.....
have a look:
https://www.tindie.com/products/Protofabtt/mylar-05mil-thermal-pads-to220--to247218-to-3/thx
Ancel