Broken rib dressed in iron material (5)
I believe the answer is:
fibre
'material' is the definition.
(I know that fibre is a type of material)
'broken rib dressed in iron' is the wordplay.
'broken' indicates an anagram.
'dressed in' is an insertion indicator (inserted letters are dressed in others).
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'rib' anagrammed gives 'ibr'.
'ibr' placed inside 'fe' is 'FIBRE'.
(Other definitions for fibre that I've seen before include "Dietary material; thread" , "In brief, a thread" , "Texture - strength of character" , "Thread, filament" , "Thread - strength of character" .)