Material I mend badly (5)
I believe the answer is:
denim
'material' is the definition.
(type of fabric)
'i mend badly' is the wordplay.
'badly' is an anagram indicator.
'i'+'mend'='imend'
'imend' with letters rearranged gives 'DENIM'.
(Other definitions for denim that I've seen before include "Mined badly for a hard-wearing fabric" , "dark blue material" , "Twilled cotton fabric" , "Hard-wearing blue fabric" , "Mined (anag)" .)