Abstract: The present invention is a process for the cryogenic separation of air to recover at least one of its constituent components, which is carried out in an air separation unit having at least one distillation column; wherein the distillation column has at least two mass transfer sections, wherein, in each mass transfer section, a flow of vapor and a flow of liquid are counter-currently contacted to accomplish mass transfer and the flow of vapor or liquid or vapor and liquid is different in one section as compared to the other section; wherein contact of the flows of vapor and liquid in each mass transfer section is accomplished using a structured packing; wherein the structured packing comprises elements which are corrugated with substantially parallel corrugations, wherein the parallel corrugations have a longitudinal axis at an angle .beta. relative to horizontal and wherein each corrugation when approximated to be a triangular cross-section has a crimp angle .alpha.