Hairy layer (4)
I believe the answer is:
fuzz
'hairy layer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fuzz that I've seen before include "Old Bill (slang)" , "Frizzy mass of hair" , "lack of clarity" , "Soft, fine hair; blur" , "Frizzy hair; blurred image" .)