Herein, this research focuses on a series of hybrid epoxy materials containing modifiers based on open-cage silsesquioxanes. The study involves the synthesis of various open-cage silsesquioxanes (via hydrosilylation reaction) featuring extended epoxy groups, allowing for cross-linking with epoxy resin and an amine hardener. The core structure of silsesquioxanes and the linker length and nature between the IC-POSS (incompletely condensed silsesquioxane) framework and epoxy group are crucial parameters affecting the cured material properties. This article presents a comprehensive investigation into the synthesis, characterization, and impact of epoxy-functionalized open-cage silsesquioxane modifiers on epoxy resin properties (morphology, thermal, surface, and mechanical properties), offering valuable insights into developing epoxy cured composites.