A facile and cost-effective modified sol–gel synthesis is employed to synthesize flexible silica-cellulose hybrid aerogels (SCHA) using recycled cellulose fibers (RCF). The effect of cellulose fiber concentrations and ambient temperature conditions on the thermal, acoustic, and oil absorption characteristics was quantified comprehensively. The experiments were conducted by considering the range of weight fractions from 1–4 wt.% from waste tissue paper with a cross-linker and tetraethylorthosilicate (TEOS) as silica precursors. The SCHA aerogels were modified by a silylating agent with surface hydroxyl groups to achieve superhydrophobic behavior with a water contact angle (WCA) as high as 168°. The synthesized aerogels were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), and Brunauer-Emmett-Test (BET) to identify the physical morphology. An excellent oil absorption capacity of 24.8 g.g−1 was also noticed with 4 wt.% of cellulose concentration in hybrid aerogel retained up to 5 cycles with an absorption capacity of 6.4 g.g−1. The average thermal conductivity of hybrid aerogels was estimated in the range of 0.038–0.032 W/m K. Slight enhancement in the thermal conductivity is noted with the increase in wt.% of cellulose to the silica aerogel. However, about 40–50 °C improvement in thermal degradability (as concluded from Thermogravimetric Analysis) with a minimum weight loss was observed in hybrid aerogel over cellulose aerogel. A comparatively high sound absorption coefficient of 0.453–0.628 at low frequency (1500 Hz) and 0.86–0.94 at high frequency (3600 Hz) was achieved with an average thickness of 8 mm compared to cellulose aerogel. The compressive Young’s modulus of hybrid aerogels was also enhanced by 94.12%. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.