Used more ply and plastic (7)
I believe the answer is:
polymer
'plastic' is the definition.
(thesaurus)
'used more ply' is the wordplay.
'used' indicates anagramming the letters.
'more'+'ply'='moreply'
'moreply' is an anagram of 'POLYMER'.
'and' is the link.
(Other definitions for polymer that I've seen before include "Substance such as nylon" , "Material" , "Mo, reply to the large molecule" , "Resin base" , "Eg, protein, rubber etc." .)