Chambray once used to protect fabric (5)
I believe the answer is:
rayon
'fabric' is the definition.
(I know that rayon is a type of fabric)
'chambray once used to protect' is the wordplay.
'to protect' says the answer is hidden in the clue (the answer is protected by the clue).
'RAYON' can be found hidden inside 'chambray once used'.
(Other definitions for rayon that I've seen before include "Artificial material" , "Artificial fibre" , "Material - or any (anag)" , "Synthetic silk-like fabric" , "Synthetic fibre" .)