Since this came back up I looked at the package of what I was calling Acetate. It is from NENSCO and is called "Antistatic clear base" PSTAT AS7 17 #210938.
NENSCO is New England Newspaper Supply Co. and they are out of business. Google finds no results.
If the stuff works well, then it is not really important what type of plastic it is, but OTOH, it would be interesting to find out if it is PET, Mylar, Polypropylene, or whatever. What gets me is calling all clear films "Acetate".