Layer on the inner surface (6)
I believe the answer is:
lining
'layer on the inner surface' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lining that I've seen before include "waistcoat material" , "Jerome Kern song: 'Look for the silver . . . . . . '" , "Old song: 'Look for the silver . . .'" , "It's found on the inner side of a garment" , "Heather is wearing fashionable" .)