Packaging material (9)
I believe the answer is:
polythene
'packaging material' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for polythene that I've seen before include "A lightweight thermoplastic" , "A light plastic material used for wrapping" , "Synthetic 6 Dn" , "Packaging material -- telephony (anag)" , "Synthetic thermoplastic used for packaging, etc" .)