Mass transfer apparatus having a structured packing

An absorber or desorber contains a layer (10) for a structured packing having a wave-like profile, wherein a plurality of open channels (12, 14, 16) is formed due to the wave-like profile. According to the invention, said open channels have a first wave trough (22), a first wave peak (32) and a second wave peak (42). The first wave peak (32) and the second wave peak (42) delimit the first wave trough (22), the first and second wave peaks having a first apex (33) and a second apex (43). A depression (34) extending in the direction of the first apex (33) is formed on the first apex (33) of the first wave peak (32). The first wave trough (22) has a trough bottom (23), wherein the normal distance (27) from at least one point of the depression (34) to the trough bottom (23) of the wave trough (22) is smaller than the normal distance (28) from the first apex (33) to the trough bottom (23) of the wave trough (22).