Abstract: A rotating kiln or cooler for use in the manufacture of cementitious materials comprises a tubular body (1) mounted for rotation about the longitudinal axis thereof, a material being fed into the body at one end and removed at the other end. Air or combustion gases flow through the body (1) in the opposite direction to the material.In order to improve the heat transfer between the material and the air or gases, at least one ring (12) of lifting members (34) is provided on the interior periphery of the body (1). The members (34) lift the material and allow it to drop back to the bottom of the kiln, thus increasing the surface area of the material in contact with the air or gases.