Fibres woven into underwear (6)
I believe the answer is:
briefs
'underwear' is the definition.
(I've seen this before)
'fibres woven' is the wordplay.
'woven' is an anagram indicator.
'fibres' with letters rearranged gives 'BRIEFS'.
'into' acts as a link.
(Other definitions for briefs that I've seen before include "Garments" , "Case summaries drawn up for barristers" , "Instructs a barrister" , "by which privates will be constrained" , "Underpants for a lawyer" .)