An evaporative cooling pad for an air treatment unit includes a first set corrugations defined in a direction transversely of a horizontal plane of the pad, the sheets of the first set being disposed alternatively with the sheets of the second set, with the corrugations of the first set crossing the corrugations of the second set; the crossed corrugations defining passageways penetrating from a first edge to a second edge of the pad, the corrugations of the corrugated sheets bearing against one another so that the sheets touch where at least one of the wave peaks (p1) and wave troughs (t1, t2) of their respective corrugations cross; at least one wave peak (p2) between two wave peaks (p1) of equal amplitude (a1) of at least one of the first and second set of corrugated sheets has a smaller amplitude (a2) than the wave peaks (p1) of equal amplitude (a1).