Study setter's material (5)
I believe the answer is:
denim
'material' is the definition.
(type of fabric)
'study setter's' is the wordplay.
'study' becomes 'den' (term for a study or office).
'setter's' becomes 'im' (I am - referring to the crossword setter).
'den'+'im'='DENIM'
(Other definitions for denim that I've seen before include "Hard-wearing cloth" , "Mined (anag)" , "Twill cloth" , "Hard-wearing material seen in jeans" , "Twilled cotton fabric" .)