In order to determine the silica content in the composites, TGA measurement was carried out in air. Figure 5 shows the TGA curves of CP2, CP4, CP20 and CP22. In these samples, the thermal degradation occurs mainly at about 324 °C, but the most interesting point is the residual weight remaining at 500 °C. The composite CP20 of C20 matrix and ASi reinforcer contains residual weight of 47.3%, that is close to the nominal 50 wt % remanent according to the formulation indicating that this composite released 2.7 wt % more than expected. On the other hand, composite CP22 of AG20 matrix and ASi reinforcer contains residual weight of 53.7% indicating that this formulation retained 3.7 wt %, possibly due to the inorganic particles stabilization into the matrix fibers net. About composite CP2 of C20 matrix and NSi reinforcer according to the formulation 50 wt % of residual silica content must be expected, but this sample retains only 41% indicating again that 9% is released in excess, akin to CP20. In such C20 matrix samples, an excess of mass is released after 500 °C treatment. On the contrary, composite CP4 of AG20 matrix and NSi reinforcer releases only 38 wt % retaining 62 wt %, meaning that 12% more weight is retained in this composite in comparison with the calculated content of silica. An excess of weight is found in the composites of AG20 matrix after 500 °C treatment as in the case of CP22. An explanation of this large amount of residual mass in CP4 could relay in the thermal capability of NSi that can be shielding the composite matrix avoiding its complete thermal degradation due to the chemical functionalization of NSi that it is not the case for ASi.