Since rasching rings were first used in the early 1900’s, a number of different random packing types have been developed and used. Random packing is a type of randomly putting packing into the tower, and has various sizes ranging from 1/4 inch to 3 inch. In general, random packing is comparably free from material selection limited by the features of the system.
In the case of the same kind of packing, if the size gets bigger, efficiency gets lower because pressure loss decreases, process capacity increases, but contact surface areas lessen.
The most common types are pall rings which are widely well-known. Recently, NMTP is frequently used which has high void fraction and low aerodynamic drag of the saddle shape.