The most common and most likely answer to this crossword clue is the 8 letter word PELLICLE
I've seen this crossword clue in The Guardian
P
E
L
L
I
C
L
E
Buddy explains!

The straight part
We know that "film" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case film = pellicle.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PELLICLE mean?
PELLICLE noun- A thin skin or film.
- A skin or coating of proteins on the surface of meat to be smoked, improving the surface adhesion.
- Cuticle, the hard protective outer layer of certain life forms.
- The skin of a mushroom cap.
- The outermost layer of a mushroom, often used only for a surface that is viscid and easily peels off.
- The growth on the surface of a liquid culture.
- The photosensitive emulsion of photographic film.
- A thin plastic membrane used as a beam splitter or protective cover.