A decanter centrifuge (1) has a rotor comprising a helical conveyor (2) and a drum (20). The conveyor (2) comprises a conveyor hub (3) and helical flights (4), and the drum comprises an inner shell (21) of steel and an outer shell (22) of fiber reinforced plastic. The conveyor (2) consists of a shaft of tube form (11), primarily made from carbon fiber reinforced resin, and helical flights (4), primarily made from polyurethane. The flights (4) of the helical conveyor are formed in such a way that they all the time is in contact with the inner periphery of the drum (31). The division of the drum in an inner and an outer shell causes the mass of the drum to be reduced considerably.