In this manuscript a series of cubic silsequioxane monomers with their eight vertices functionalized by different organic tethers and terminated with triethoxysilane groups were acid hydrolyzed, spin cast, and vitrified into hard organosilicate films. Both the length of the organic ligands and the number of triethoxysilane groups were varied to change the degree of cross-linking and cubic silsequioxane content of the vitrified films. This resulted in a series of high-quality optical-grade coatings with excellent properties. In general, higher concentrations of the cubic silsequioxane moiety in the network and higher cross-link densities led to enhanced mechanical properties, lower porosity, higher density, lower thermal expansion, and a very hydrophilic surface. The manner by which these properties can be tuned via the cubic silsesquioxane content is discussed in comparison to the structure–property relations for other spin on silsequioxane type films. Copyright © 2013 John Wiley & Sons, Ltd.