Border of the material (3)
I believe the answer is:
hem
'border' is the definition.
(I've seen this in another clue)
'of the material' is the wordplay.
'of' indicates a hidden word.
'HEM' can be found hidden inside 'the material'.
(Other definitions for hem that I've seen before include "try to attract attention" , "Express hesitation" , "Part of skirt" , "Border; fringe" , "Sewn border" .)