Half of coat in spotted material (6)
I believe the answer is:
sateen
'material' is the definition.
(I know that sateen is a type of material)
'half of coat in spotted' is the wordplay.
'half of' suggests halving the letters.
'in' means one lot of letters goes inside another.
'spotted' becomes 'seen' (I've seen this in another clue).
'coat' halved is 'at'.
'at' going inside 'seen' is 'SATEEN'.
(Other definitions for sateen that I've seen before include "Closely woven cotton fabric resembling satin" , "Glossy cotton fabric" , "Sea net could provide a glossy fabric" , "Shiny cloth found in senate" , "Cotton fabric with a shiny finish" .)