The development of mechanically robust, visibly transparent and infrared spectrally selective films is pivotal for enhancing the thermal insulation efficiency of transparent building envelopes such as skylights and windows. Herein, an aligned nanofiber-aerogel-reinforcing all-polymeric nanocomposite is prepared by impregnating and curing methacrylate monomers within an aligned cellulose nanofiber aerogel. The deliberately structured cellulose aerogel with an aligned porous structure perpendicular to the film plane facilitates the formation of a robust nanofiber-matrix interface within the nanocomposite. This design enhances the mechanical strength and impact resistance reaching values of 274.5 MPa and 51.1 kJ m−2, respectively. Utilized as spectrally selective transparent window materials, these nanocomposites demonstrate exceptional infrared spectral selectivity, with a visible light transmittance of up to 78.2 %, near-infrared transmittance as low as 32.3 %, and mid-infrared emissivity as high as 91.0 %. They can be directly utilized as high-strength and impact-resistant spectrally selective cooling windows for effective indoor solar energy management, offering both indoor illumination and spontaneous cooling, leading to a reduction in indoor temperatures by 3.2 °C compared to conventional glass window materials.