Material extracted from below (5)
I believe the answer is:
denim
'material' is the definition.
(type of fabric)
'extracted from below' is the wordplay.
'extracted' becomes 'mined' (to mine is to extract something from a mine).
'from below' says the letters should be written backwards (in a down clue, letters go up).
'mined' reversed gives 'DENIM'.
(Other definitions for denim that I've seen before include "Twilled cotton fabric" , "Tough cotton fabric" , "Mined badly for a hard-wearing fabric" , "Twill cloth" , "maker of jeans" .)