...There has been one attempt in history of a company converting 135micron thick triacetate into 120 films and the the product showed severe problems. There were thousands of claims....No other manufacturer ever did this....All larger manufacturers use:
100 micron PET or triacetate for 120 film
135 micron triacetate (greybase or clear) for 35mm film
170 micron PET or triacetate for sheetfilm...
It's 125 micron, not 135, but Ilford uses the same acetate master roll for both 35 mm and 120 Delta 3200. See the second and third paragraphs on page one here: