So i bought a kapton foil heater, 250x200mm,

So i bought a kapton foil heater, 250x200mm, and wanted to replace the wires on it with something better. But after removing the stock wires, I couldn’t get the new solder to wet/flow into the foil.
So any hints / tips on how to solder to this? Any idea what material the foil is made of?

It could be nichrome or stainless steel.

Thats what I think. If it’s nichrome then good luck. If it’s stainless then I guess I need acid flux?

Clean the pads real well then lots of flux!

I found that acid flux worked. I think it was stainless.

Be sure to very thoroughly clean off the acid flux afterwards. Residual acid flux can corrode electrical connections, so it isn’t commonly used there.