Wood inside the plastic protective covering (6)
I believe the answer is:
helmet
'protective covering' is the definition.
(helmet is a kind of protective covering)
'wood inside the plastic' is the wordplay.
'wood' becomes 'elm' (elm is a kind of wood).
'inside' indicates putting letters inside.
'plastic' indicates anagramming the letters (plastic can mean easily moulded).
'the' with letters rearranged gives 'het'.
'elm' going within 'het' is 'HELMET'.
(Other definitions for helmet that I've seen before include "Protective head-covering for armour or motor cyclist" , "Hard hat" , "personal protection" , "Tin hat" , "Police hat" .)