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

The straight part
We know that "Materials" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case materials = plastics.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 PLASTICS mean?
PLASTICS noun- A synthetic, solid, hydrocarbon-based polymer, whether thermoplastic or thermosetting.
- (metonym) Credit or debit cards used in place of cash to buy goods and services.
- Fakeness, or a person who is fake or arrogant, or believes that they are better than the rest of the population.
- An instance of plastic surgery.
- A sculptor, moulder.
- Any solid but malleable substance.
- Plastic surgery, especially as a profession.