Silica aerogels are well-known ultra-light materials with potential applications such as thermal superinsulation (thermal conductivity at ambient conditions < 0.020 W.m-1.K-1), but their mechanical fragility limits their large-scale usage. To reinforce silica aerogels, we used cellulose aerogel (“aerocellulose”) as a reinforcing matrix. We describe the synthesis and properties of new hybrid cellulose-silica aerogels prepared by impregnation of cellulose alcogel by a polyethoxydisiloxane sol, followed by drying with supercritical CO2. Two impregnation routes were tested: diffusion-controlled and introduction of sol into matrix by forced flow; the latter strongly decreased the impregnation time. Nanostructured organic-inorganic aerogels made of interpenetrated cellulose and silica networks were obtained. The apparent density of the hybrid materials was between 0.1and 0.2 g/cm3 and the BET specific surface area increased from about 250-300 cm2/g for aerocellulose to 700-800 cm2/g for the hybrid organic-inorganic aerogels, confirming the formation of a silica aerogel network in the pores of the aerocellulose matrix. Hybrid aerogels were also prepared from chemically hydrophobised cellulose and silica; they show contact angle with water of 140. Research leading to these results was funded within the 7th EU Framework Program, (FP7/2007-2013), under grant agreement n260141, AEROCOINS project.