Water-cast films of two ethers of cellulose, hydroxypropylcellulose (HPC) and hydroxyethylcellulose (HEC), with dispersed silica particles, were deposited on flat substrates. X-ray specular reflectivity was used to characterize the structure of these solid ca. 1000 Angstrom thick films as a function of the added colloidal fraction. It was shown that the structural changes resulting from increasing amounts of incorporated silica particles pass through distinctively different routes in the case of HPC- and HEC-based films. However, the structures in the two cases are similar at sufficiently high colloidal fraction. (C) 2004 Elsevier Ltd. All rights reserved.