Synthetic rubber (8)
I believe the answer is:
neoprene
'synthetic rubber' is the definition.
(neoprene is a kind of synthetic rubber)
This is the entire clue.
(Other definitions for neoprene that I've seen before include "Synthetic like rubber" , "Synthetic rubber-like polymer" , "Synthetic polymer; none peer (anag.)" , "Synthetic rubber - ne'er open (anag)" .)