That Kapton polymide stuff is one sided adhesive, and I see that they do not do a size about 18mm wide.
Here is a paragraph, rough draft, from my book I am doing regards me making the OzInverter No1 and the Big No 2.
"Mylar tape, or Molinex, Nomex ? my observations.
The trick is keeping it tight, and wrapping it right, let it go or drop the bobbin and a birds nest ensues.....
I obtained 200m 18mm wide and 0.085mm thick from the supplier of my toroid bare cores, but sadly it was not enough but was just correct for thickness.
The PowerJack toroid I dismantled had super thin stuff, 0.065mm, that very easily broke, but I managed to salvage most in small runs, I just used the adhesive backed Mylar tape to do the joins.
The Mylar tape I get from the USA......
http://www.ebay.co.uk/itm/181696004499?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT ..... is 0.125mm thick, but i found that it is just to thick.
Especially when its not flexible enough to allow the next winding of the secondary to fit down in the gap of the previous winding, especially on the internal centre hole windings. But it does come oval shape and goes down a 62mm dia hole okay without having to unwind..........
I half lap the Mylar tape on its self on the exterior of the toroid, and I do 2off complete wraps as a minimum, with the super thin breaking stuff I did 3off wraps, Waste not.
Don't forget the epoxy resin on each secondary winding before you cover it with Mylar tape. I like the thin viscosity stuff that I mix and lightly paint on.
I have some thin Molinex sheet that I put under the whole toroid to collect any excess resin.
The following evening turn the toroid over, peel off the Molinex sheet, Mylar tape on the hardened, but still soft, epoxy resin coated winding, and then next copper wire winding goes on."
As I said I could do with another Mylar supplier source, 800 meters, at about 0.085mm thick and 18mm wide.
I trust this helps?