Abstract: Heat and/or mass exchanger operating by direct contact between a liquid and a gas comprising a cooling tower, of the type having a casing in which is disposed a filling through which the liquid and the gas circulate. The filling is constituted of a plurality of independent tubular elements whose cross-section varies along the length of the tubular elements. The tubular elements are preferably disposed with their axes vertical and parallel to define internal and external passages of variable section. The tubular elements vary in cross-section in continuous manner throughout their length and the section variations recur periodically along the length of the tubular elements.