Increasing noise pollution has generated a tremendous threat to human health and incurred great economic losses. However, most existing noise-absorbing materials present a significant challenge in achieving lightweight, robust mechanical stability, and efficient low-frequency (<1000 Hz) noise reduction. Herein, we create highly compressible micro/nanofibrous sponges with thin-walled cavity structures for efficient noise reduction through electrospinning and dispersion casting. Manipulating the phase separation driven by solution/water interaction in jets enables formation of fluffy fibrous frameworks, on which the deformation of casting dispersion is controlled to develop thin-walled cavity structures consisting of semiopened cells and entangled networks. The resultant sponges exhibit lightweight characteristics (2.2 mg cm–3) and mechanical robustness, integrated with remarkable low-frequency noise reduction capability (absorption coefficient up to 0.98) benefiting from vibration and viscous friction effects of cavity-structured skeletons. This work may offer new horizons for designing advanced fibrous acoustical materials, inspiring next-generation noise-reducing devices in aerospace and transportation.