2. Results and Discussion 2.1. Microstructure and Composition Analysis Firstly, pure silica aerogel (named Si/PI-0) with high porosity was prepared using the sol–gel method (Figure 2a,b). Subsequently, a solution of polyimide precursor (polyamic acid) at a specific concentration was impregnated into the silica pores. Within these pores, the polyamic acid underwent in situ polymerization to form a PI nanofiber gel, ultimately resulting in the composite aerogel Si/PI-6, as depicted in Figure 2c,d.