Rotten sneak given fleece clothing material (9)
I believe the answer is:
snakeskin
'clothing material' is the definition.
(I know that snakeskin is a type of clothing material)
'rotten sneak given fleece' is the wordplay.
'rotten' indicates an anagram.
'given' is a charade indicator (letters next to each other).
'fleece' becomes 'skin' (I've seen this in another clue).
'sneak' is an anagram of 'snake'.
'snake'+'skin'='SNAKESKIN'
(Other definitions for snakeskin that I've seen before include "Expensive leather from reptiles" , "that may be cast off" .)