I mend split material (5)
I believe the answer is:
denim
'material' is the definition.
(type of fabric)
'i mend split' is the wordplay.
'split' indicates anagramming the letters (letters split up and reassembled).
'i'+'mend'='imend'
'imend' is an anagram of 'DENIM'.
(Other definitions for denim that I've seen before include "Hard-wearing material seen in jeans" , "Durable material" , "Thick cotton cloth" , "Cloth for jeans, etc" , "maker of jeans" .)