Nothing reflected in French material (5)
I believe the answer is:
linen
'material' is the definition.
(linen is a kind of material)
'nothing reflected in french' is the wordplay.
'nothing' becomes 'nil' ('nil' can be a synonym of 'nothing').
'reflected' says the letters should be written in reverse.
'in french' becomes 'en' ('en' can be French for 'in' e.g. en France).
'nil' written backwards gives 'lin'.
'lin'+'en'='LINEN'
(Other definitions for linen that I've seen before include "Lenin (anag) -- fabric" , "given blanket coverage" , "Cloth woven flax fibres" , "Tablecloth material" , "Bed sheets etc" .)