Abstract: The fill slat for use in water cooling towers comprises a perforated body portion, a central longitudinal rib, and downwardly inclined side flanges. The rib is inverted v-shape in cross-section and functions as a rigidifying beam for the fill slat. The rib is open at its bottom, thereby permitting a plurality of fill slats to be nested to reduce shipping costs. The side flanges are formed with slots, certain of which are angled, to receive the supporting wires. A holding clip can be additionally provided to reduce rolling or longitudinal movement of the fill slat.