Material for back fat cheese (7)
I believe the answer is:
'material' is the definition.
(I know that taffeta is a type of material)
'back fat cheese' is the wordplay.
'back' says the letters should be written backwards.
'cheese' becomes 'feta' (type of cheese).
'fat' backwards is 'taf'.
'for' is the link.
(Other definitions for taffeta that I've seen before include "Lustrous silky fabric" , "A shiny silklike fabric" , "silky stuff" , "Fabric - fat fate (anag)" , "Crisp, smooth, lustrous fabric" .)