Material gained by Interpol yesterday (9)
I believe the answer is:
polyester
'material' is the definition.
(I know that polyester is a material)
'gained by interpol yesterday' is the wordplay.
'gained by' says the answer is hidden in the clue.
'POLYESTER' can be found hidden inside 'interpol yesterday'.
(Other definitions for polyester that I've seen before include "Synthetic compound" , "Turn to Presley for the synthetic fabric" , "Synthetic textile" , "Synthetic fibre or substance" , "Man-made fibre" .)