About the thermal stability of cellulose/silica hybrid composites, created by a sol-gel method using TEOS precursor of silica, bleached pulp and tungstophosphoric acid (H3PW12O40) (EPTA). The thermal degradation of the organic material was observed at 305 °C and at 345–350 °C for the hybrid materials indicating that with 51% (wt/wt) of SiO2 content in the cellulosic composites clearly confers higher thermal resistance to those materials. This communication also relates the thermal conductivity coefficient of these materials with the effect of silica content showing its capacity as conventional insulation material .