In this study, X-ray computer tomography and light-induced fluorescence were applied to investigate the morphology of liquid flow inside structured packing. Fluid dynamic parameters such as liquid holdup and wetted surface were determined to study the effect of the variation of viscosity and liquid load. Flow patterns inside the packing were identified and categorized. Liquid film thickness and its distribution were analyzed On single sheets. For both methods, the Measured holdup values are in good agreement, despite differences in the techniques of measurement. For the flow patterns and their relative contribution, as well as mean liquid film thickness, a strong dependency on the varied parameters was found. Furthermore, the density function of film thickness distribution changed characteristically with liquid load and viscosity. The complementary use of tomography and optical assessment allowed an improved insight into flow phenomena and the observed interdependency of physical, geometric, and operational parameters.