In this article, silica sol (diameter: 8100 nm) and polymer latex (Tg < 25 degrees C) were mixed and dried at room temperature to prepare nanocomposite films with high silica load (50 wt %). Effects of silica size, silica load, and the Tg of the polymer on the film-forming behavior of the silica/polymer latex blend were investigated. The transparency, morphology, and mechanical properties of the nanocomposite films were examined by UVVis spectroscopy, SEM, and nanoindentation tests, respectively. Transparent and crack-free films were produced with silica loads as high as 70 wt %. Thirty nanometers was found to be the critical silica size for the evolution of film-forming behavior, surface morphology, and mechanical properties. Colloidal silica particles smaller than this critical size act as binders to form strong silica skeleton. This gives the final silica/polymer nanocomposite film its porous surface and high mechanical strength. However, silica particles with sizes of 30 nm or larger tend to work as nanofillers rather than binders, causing poor mechanical strength. We also determined the critical silica load appeared for the mechanical strength of silica/polymer film at high silica load. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013