Light support: Regenerated cellulose gel prepared from an aqueous alkali–urea solution serves as scaffold/template for the in situ preparation of cellulose–silica composite aerogels (see picture) by a sol–gel process from organic silicates, and drying with supercritical CO2. The resulting composite aerogels have the mechanical strength and flexibility, large surface area, semi-transparency, and low thermal conductivity of the cellulose aerogels.