Abstract: A heat exchange element is described having adjacent, heat-transferring, smooth walls (1) which, between each other, delimit flow channels (4) with preselected channel widths (B) for at least one fluid and are provided with undulations (6) which protrude on both sides and transversely relative to imaginary central planes (7), said undulations having preselected wavelengths (?) as well as apexes (9a, 9b) with radii of curvature (R) and apex spacings (W) measured transversely relative to the central planes (7). According to the invention inequalities 0.1?B/W?0.55 and R?1.2 B apply at least partially to ratios of channel width (B)/apex spacing (W) and channel width (B)/radius of curvature (R) (FIG. 2).