Imperfections — bedding material must be sent back (5)
I believe the answer is:
warts
'imperfections' is the definition.
(wart can mean an imperfection or flaw)
'bedding material must be sent back' is the wordplay.
'bedding material' becomes 'straw' (straw is used for animal bedding).
'must be sent back' says the letters should be written backwards.
'straw' back-to-front is 'WARTS'.
(Other definitions for warts that I've seen before include "Verrucas" , "feature prominently on 12,14 across [UGLY SISTERS]" , "Skin growths" , "unwanted lumps" .)