Sandwich packings are innovative column internals consisting of two layers of ordinary packing with different geometrical surface area. The layer with the high surface area, hold-up layer, has a lower flooding point as compared to another, de-entrainment layer. Sandwich packings can be operated even when the hold-up layer is flooded. In operation, different fluid dynamic regimes occur along the column. The flow in the flooded hold-up layer is comparable with that in trays. A froth regime is established above the hold-up layer, whereas a film flow develops in the remaining part of the de-entrainment layer. The proper design of sandwich packings requires a mass transfer model capable of considering all these different regimes. In this work, the rate-based concept is used to develop a mass transfer model of sandwich packings. This model employs two alternate column segments. One of them corresponds to de-entrainment layer, and here, mass transfer correlations for packed columns are applied. Another segment is related to the hold-up layer; it is described with correlations for sieve tray columns. The developed mass transfer model is validated with experimental efficiency data for sandwich packings. (C) 2015 Elsevier B.V. All rights reserved.