Packing material for eccentric directors (9)
I believe the answer is:
cardboard
'packing material' is the definition.
(cardboard is a kind of packing material)
'eccentric directors' is the wordplay.
'eccentric' becomes 'card' (card can mean an eccentric person).
'directors' becomes 'board' (board of directors).
'card'+'board'='CARDBOARD'
'for' is the link.
(Other definitions for cardboard that I've seen before include "stiff material" , "A stiff thick paper" , "without substance" .)