Cellulose aerogel, as a lightweight, highly porous, and renewable biomass-derived material, has witnessed rapid development in thermal insulation applications. This chapter reviews its research progress in the field of thermal insulation. Based on the macroscopic morphology, cellulose-based aerogels (CBAs) are categorized into one-dimensional (1D) aerogel fibers, two-dimensional (2D) aerogel films, and three-dimensional (3D) bulk aerogels. Here, their preparation methods are summarized first, followed by a review of their application areas. Their primary applications include building insulation, textile filling, and infrared stealth thermal management. Research indicates that structural regulation and functional modifications (e.g., hydrophobic treatment, compositing with nanoparticles) significantly enhance the mechanical strength and environmental adaptability of these three material types. Future efforts need to focus on optimizing scalable manufacturing processes and reducing costs to facilitate industrial application.