Fluffy, vacuously frilly with internal deficit (6)
I believe the answer is:
flossy
'fluffy' is the definition.
(I know that fluffy can be written as flossy)
'vacuously frilly with internal deficit' is the wordplay.
'vacuously' suggests removing the centre.
'with internal' is an insertion indicator.
'deficit' becomes 'loss' (I've seen this before).
'frilly' with its middle removed is 'fy'.
'fy' enclosing 'loss' is 'FLOSSY'.
(Other definitions for flossy that I've seen before include "As soft as down" , "Like silk" .)