Abstract: A packing for a vessel to contact fluid therein wherein the packing comprises a plurality of insert units, each insert unit comprising a plurality of transversely extending elements disposed longitudinally along the insert unit and angularly thereabout wherein a portion of each transverse element lies in close proximity to a first individual conceptual surface characterized in that the insert units are disposed in side-by-side relationship in a regular manner and the cross-sectional area between adjacent individual conceptual surfaces of adjacent insert units at least at one position longitudinally of the plurality of insert units is no greater than the maximum cross-sectional area within an individual conceptual surface of an insert unit between two adjacent transversely extending elements thereof at any cross-section longitudinally of the plurality of units.