Study writer's material (5)
I believe the answer is:
denim
'material' is the definition.
(type of fabric)
'study writer's' is the wordplay.
'study' becomes 'den' (term for a study or office).
'writer's' becomes 'im' ('I am' referring to the writer of the clue).
'den'+'im'='DENIM'
(Other definitions for denim that I've seen before include "Coloured cotton twill" , "maker of jeans" , "Hard-wearing clothing material, twilled cotton" , "Hard-wearing blue fabric" , "Thick cotton cloth" .)