Slicker material (7)
I believe the answer is:
oilskin
'slicker material' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oilskin that I've seen before include "Waterproof cloth as for sailors" , "Protective coat" , "protection for Ainslie?" , "Waterproof cloth for rain-gear" , "Heavy-duty waterproof" .)