Study this writer's material (5)
I believe the answer is:
denim
'material' is the definition.
(denim is a kind of material)
'study this writer's' is the wordplay.
'study' becomes 'den' (I've seen this before).
'this writer's' becomes 'im' (the person writing the crossword clues**).
'den'+'im'='DENIM'
(Other definitions for denim that I've seen before include "dark blue material" , "Cotton twill fabric" , "Mined badly for a hard-wearing fabric" , "Hard-wearing blue fabric" , "Coarse durable twill-weave cotton fabric" .)