Material in paper, along with unknown article (7)
I believe the answer is:
organza
'material' is the definition.
(organza is a kind of material)
'paper along with unknown article' is the wordplay.
'paper' becomes 'organ' (I've seen this in other clues).
'along with' says to put letters next to each other.
'unknown' becomes 'z' (algebra).
'article' becomes 'a' (English indefinite article).
'organ'+'z'+'a'='ORGANZA'
'in' is the link.
(Other definitions for organza that I've seen before include "Stuff" , "dress material" , "Thin stiff dress fabric" , "Silky fabric" , "Silk (or silk-like) fabric" .)