Boehmite nanomaterials have been researched for use in applications such as separation media, fillers for resins, and catalyst support. This study investigates the relationship between structural density and mechanical and thermal performance of boehmite nanofiber-polymethylsilsesquioxane (PMSQ) composite aerogels. Tri-functional organosilicon alkoxide methyltrimethoxysilane (MTMS) was added to a boehmite nanofiber aqueous dispersion; the colloidal nanofibers were coated and bonded with polymethylsilsesquioxane, to produce transparent to translucent wet gel monoliths. Low bulk density aerogel panels were prepared by CO2 supercritical drying of the wet gel monoliths before their mechanical properties and thermal conductivity were investigated. As the amount of the MTMS in the starting composition increased, the fibrillar monolith skeleton coated with PMSQ thickened. Correspondingly, the Young's modulus of the monoliths increased, and the thermal conductivity decreased. When the amount of MTMS added was small, it was possible to deform the translucent panels by uniaxial compression. After 30% uniaxial compression of the panel, the thermal conductivity was suppressed by 19%. The thermal conductivity response to compressive deformation of fibrous aerogels, after fabrication, may inform future insulation material development.