A facile method to synthesize light weight thermally superinsulating composite aerogel is being presented here. A polymethylsilsesquioxane (PMSQ) – cellulose composite aerogel starting from a trifunctional precursor viz. methyltrimethoxysilane (MTMS) and kapok fibers have been synthesized. Kapok fibers have been employed as they have a homogeneous hollow structure and also possess intrinsic low density. A PMSQ-Kapok composite aerogel with a density as low as 0.053 gcm−3 with a thermal conductivity of 0.018 W m−1 K−1 in room conditions has been synthesized. Besides, a flexural strength (at maximum stress) of 108 kPa ± 21 has been obtained through three points bending test. All the composite aerogels are mesoporous as characterized by N2 sorption isotherms and hydrophobic as shown by sessile drop experiments. On comparison with the earlier reported works and with some of the commercially available aerogel composites, the current results seem promising. For demonstrating the real application purpose, thin composite aerogel sheets have also been synthesized which could be easily rolled/bended.