The typical Packed Distillation column has one or more beds, each consisting of packing, a support plate, a bed limiter or a hold down plate, and a liquid distributor, and other liquid and vapor inlets and outlets may also be required.

In a packed column, liquid and vapor flows counter currently and mass is transferred between the two phases continuously. In contrast, mass transfer in a trayed column 
occurs more stage wise, as the liquid flowing across a tray comes in contact with vapour rising through the tray, after which the liquid and vapor separate for for transport to the next trays.

Gravity is the driving force for the liquid, and pressure differential for the vapor, the latter overcoming the drag resistance of the packing, the liquid and the internal structures. Liquid occupies only as much space as necessary to flow through the packing. The remaining cross- section of the column is available for vapor flow. In effect, the down-comer area is adjustable. This differs from the trayed column, in which down-comer dimensions are fixed.

In packed columns, surface area for heat and mass transfer between the liquid and vapor phases is provided by the liquid film, waves and droplets generated as liquid flows over and through the packing elements. For each column, there are upper and lower limits of liquid and vapor flow rates that entitles satisfactory performance.