PET film identification...Help!

Did you try to use FTIR? And DSC should be useful too for polymer identify.

You need to tell us the tools you have on hand and type of film.

Can you clarify your question?

Do you want to figure out which PET or do you simply want to confirm that your film is PET?

For the latter DSC should be sufficient.

Another way of identifying PET is the wet chemical method: Heat the film with a quantity of ethanolamine: when the solution cools, a nice crystalline mass of the amide of terephthalic acid forms.