Material that's dug up (5)
I believe the answer is:
denim
'material' is the definition.
(type of fabric)
'dug up' is the wordplay.
'dug' becomes 'mined' (dug into the ground).
'up' is a reversal indicator (in down clue: letters go upwards).
'mined' written backwards gives 'DENIM'.
'that's' acts as a link.
(Other definitions for denim that I've seen before include "Material for casual trousers or jackets" , "Hard-wearing cloth" , "Thick cotton cloth" , "maker of jeans" , "Tough cotton fabric" .)