<p>Lightweight and thermally stable ceramic nanofibrous aerogels hold great potential for applications in extreme thermal environments. Nanofibers play a crucial role in determining the microstructure and properties of the aerogels. This study prepared alumina-based nanofibers using different contents of polymer template (polyvinyl alcohol (PVA)) via electrospinning technology. Ceramic nanofibrous aerogels were subsequently fabricated using the as-prepared nanofibers via a direct foaming method, followed by freeze-drying and high-temperature sintering. The fibers exhibited increased diameter and improved thermal stability as the PVA content increased. Finer fibers, due to stronger entanglement, stabilized larger bubbles and formed denser porous networks, resulting in higher porosity and lower density. As fiber diameter increased, pore size and porosity decreased, while compressive strength improved attributed to increased inter-fiber contact area and improved structural stability due to the presence of smaller grains. Meanwhile, enhanced solid-phase heat conduction led to an increase in thermal conductivity. This study highlights the critical role of fiber dimension in regulating the structure and properties of aerogels formed by the foaming strategy and offers practical guidance for the design of high-performance ceramic aerogels.</p> Graphical Abstract <p></p>