Bog material (4)
I believe the answer is:
peat
'bog material' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for peat that I've seen before include "Fuel or compost (but no longer to be used as such!)" , "Vegetable matter in bogs, like turf" , "Fuel from marsh" , "Tape around turf" , "Bog material" .)