One clothed in extra material (5)
I believe the answer is:
moire
'material' is the definition.
(moire is a kind of material)
'one clothed in extra' is the wordplay.
'one' becomes 'i' (Roman numeral).
'clothed in' indicates putting letters inside.
'extra' becomes 'more' (both can mean additional).
'i' going into 'more' is 'MOIRE'.
(Other definitions for moire that I've seen before include "Description of wavy pattern" , "fabric" , "Watered silk" .)