Unconvincing material (4)
I believe the answer is:
lame
I believe this clue is a double definition.
'unconvincing' is the first definition.
(I've seen this in other clues)
'material' is the second definition.
(lame is a kind of material)
(Other definitions for lame that I've seen before include "Fabric interwoven with metal threads" , "(Of an excuse) unconvincingly feeble" , "Unable to walk normally" , "Halt" , "Hobbling" .)