The most common and most likely answer to this crossword clue is the 8 letter word ACETATES
I've seen this crossword clue in The Daily Telegraph
A
C
E
T
A
T
E
S
Buddy explains!

The straight part
We know that "Visual aid materials" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case visual aid materials = acetates.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 ACETATES mean?
ACETATES noun- Any salt or ester of acetic acid.
- Cellulose acetate.
- A transparent sheet used for overlays.
- Ellipsis of acetate disc: a disc of aluminium covered in a wax used to make demonstration copies of a phonograph record.