A cylindrical column used to bring about the intimate contact between a rising gas or vapour and a descending liquid typically used for a gas–liquid separation such as stripping. The vessel is packed with small objects that produce a large contact area relative to their size such as Raschig rings or Berl saddles, and are used in distillation columns and adsorption and absorption towers. The liquid descends through the packing through a tortuous route and is in intimate contact with the rising gas or vapour for the purpose of raising the mass transfer area within a limited volume. The amount of packing is determined from calculations involving the number of theoretical stages required determined from vapour–liquid equilibria and the height equivalent to a theoretical plate (HETP).