Several correlations are available in the literature for the prediction of wetted area or the effective interfacial area in packed columns. A careful examination shows considerable discrepancies in the calculated areas and conflicting predictions concerning the influence of viscosity on the interfacial areas. In this work, the effect of physical properties of liquids and of surface treatment on wetted area of structured packings was experimentally studied. Several wetting tests were performed on metallic and ceramic plates with flat, smooth or textured surfaces, using a circulation system, specially designed for this purpose. The liquid film width and thickness were measured for solutions with different surface tension and viscosities in a wide range (1 to 200 cP). The experimental results show that the liquid film width, and hence the wetted area, decreased with liquid viscosity, contrary to earlier correlations in the literature. Also the influence of contact angle is not so strong as stated in the literature for random packings. In this study, a new statistical correlation for the estimation of the wetted area and for the liquid film thickness is proposed, reflecting the measured variations with viscosity and advancing contact angles.