Despite the evolution of several new die concepts since the invention of spiral mandrel dies in the 1960s, the basic geometry of the spiral grooves themselves remained unchanged. The cross section of the groove is u-shaped, i.e. consists of a rectangular and a semi-circular area. Typically, the spiral grooves abruptly merge into the annular gap, forming sharp edges. These edges negatively affect process performance e.g. by potentially damaging the polymer chains or provoking deposits. Rounding off these edges ease the effect to some extent, but alternating the general shape of the cross section has obviously a much better potential to influence the process characteristics of the die. This paper systematically investigates spiral mandrel dies with channels of different cross-sections. The geometry from these cross-sections is directly derived from the default u-shape. The modifications made include an adjustable flank angle on one or both sides, an increased width by “stretching” the semi-circular area, and various types of fillets. To analyse the influence of these changes, CFD simulations of all variants are performed. Special attention was given to make the results comparable by correcting the depth of the different channels in a way, that the pressure drop along the spiral channel remained the same. In addition, the length of the die land between two channels was also corrected, to ensure that the overall mixing behaviour of the different die variants is comparable.