A riser sleeve (1) for using when pouring metals into a casting mould includes a riser body (2). The riser body (2) includes a riser cavity (3) for holding liquid metal and a riser opening (4) for joining the riser cavity (3) to a mould cavity of the casting mould during the casting process. The riser cavity (3) has a greater diameter than the diameter of the riser opening (4) in at least one portion, the riser body (2) is made of an insulating and/or exothermic riser material. The riser body (2) is formed as a single piece, the riser opening (4) defines an axis (5), and the riser cavity (3) is asymmetric to the axis (5).