A form of plastic (7)
I believe the answer is:
acrylic
'a form of plastic' is the definition.
(I know that acrylic is a type of acrylate polymer)
This is the entire clue.
(Other definitions for acrylic that I've seen before include "The synthetic fibre is icy, Carl" , "Shiny paint" , "Synthetic fabric" , "fibre that's synthetic" , "Synthetic resin or fibre used for textiles" .)