This confuses two different things.acetic-acid ester base.
The Kodak trade name for it's PET film base is/was "Estar".
The majority of the still films we use are on a different base - cellulose tri-acetate is used rather than PET.
I don't remember whether which of the motion picture camera stock or the motion picture print stock (respectively, the Seattle Film works negatives and slides) were on PET based (Ektar) base.