This research was directed toward a better understanding of the mass-transfer processes that occur in distillation columns containing structured packings. These packings are designed to create an-extensive gas-liquid interfacial area, through a combination of packing surface texturing and geometrical arrangement in the column. Thus, the spreading tendencies of a liquid flowing over these special surfaces represent an important factor in the choice of packing for a given separation system. Part 1 of this series of papers deals with basic relationships between the liquid and the solid surface, as indicated by the contact angle. Various liquid-solid combinations were tested for contact angle using the Wilhemy plate technique, which was found to be applicable for flat or corrugated textured surfaces. Several variables thought to affect the contact angle were studied: surface tension and viscosity of the liquid, type of metal, type of texturing, and shape of the surface. Part 2 of the series will show how contact angle can be combined with liquid flow rate and packing geometry for predicting the mass-transfer performance of a particular structured packing application.