The coalescence of droplets in fibrous filters depends on many parameters such as wettability, filter depth, flow velocity, and filter materials. The objective of this work is to determine the effect of the wettability on the coalescence mechanism. Experimental results from tests on coated glass rods are presented. Three different silanes are deposited on the glass rod surfaces to change the surface wettability. Flow of water-in-oil emulsion past the glass rods is observed. When the rod surface is wetting the dispersed phase coats the rod. When the surface is nonwetting the drops do not stick easily to the surface and do not coat it but slide around to the downstream side, where they are dragged off the rod. Such behavior is important in understanding the performance of coalescing filter media. (C) 2003 Elsevier Inc. All rights reserved.