The most common and most likely answer to this crossword clue is the 8 plus 7 letter word EXPANDED PLASTIC
I've seen this crossword clue in The Times
E
X
P
A
N
D
E
D
P
L
A
S
T
I
C
Buddy explains!
The straight part
We know that "packaging material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case packaging material = expanded plastic.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.