Thermochromic vanadium dioxide (VO 2) window coatings hold the promise of reducing the energy consumption of the built environment by passively regulating solar heat gain in response to changing conditions. Composite materials with embedded VO 2 particles have shown greatly improved optical performances compared with thin films, however they typically exhibit broadened phase transition hysteresis and gradient widths, which negatively impacts the overall performance. Here, we present a scalable one-step solution based synthesis for a thermochromic smart window coating based on a vanadium dioxide sol-gel containing silica (SiO 2 nanoparticles. We compare the performance of our nanoparticle composite with thin film VO 2 along with composites formed by mixing VO 2 and SiO 2 sol-gels and find that both composites achieve an acceptable visible transmittance (∼ 50 %) along with a comparable and competitive solar modulation (12.5 % and 16.8 % respectively), roughly double that of the plain VO 2 film (6.7 %). However, our SiO 2 nanoparticle containing composite also benefits from a narrow transition hysteresis and gradient width (9.4 • C and 2.9 • C respectively). We predict that