A relatively simple model with physically meaningful parameters has been developed to describe pressure drop across the three-levels-of-porosity (TLP) reactor. This reactor has a structured catalyst packing and is suitable for countercurrent trickle flow. The model is based on gas flow through the tortuous channels between the packing elements. The shape of these channels introduces three different contributions to pressure drop: frictional loss, expansion and contraction losses and 'zigzag' loss. The model describes pressure drop across different packings, without liquid flow, with a maximum error of 20%. The model parameters show a good agreement with values calculated with literature correlations. Irrigation of the packings leads to an additional pressure drop of ca. 2 Pa per catalyst layer, or ca. 60 Pa per meter catalyst bed. This can be explained by the presence of a thin liquid film, which reduces the cross-sectional area available for gas flow. The developed model can help to reduce the experimental effort hitherto necessary to develop novel reactor packings.