Because of the prevailing environment and energy challenges, there has been a growing interest in biobased materials for thermal insulation application. Although cellulose aerogel has been considered as an excellent thermal insulating material, its thermal conductivity is generally negatively affected by the interconnected internal pores. Herein, it is demonstrated that a cellulose nanofibril (CNF)/emulsion composite aerogel with quasiclosed internal pores can be facilely fabricated by Pickering emulsion templating and solvent exchange methods. The CNFstabilized oil-in-water Pickering emulsion (with an average diameter of 1.3 μm) can be converted into quasi-closed pores by sequential solvent exchange to acetone and tert-butanol (TBA), followed by freeze-drying from TBA to suppress the formation of large ice crystals. The presence of quasi-closed pores from emulsion templating is verified by both confocal microscopy and scanning electron microscopy images and is confirmed to reduce thermal conductivity to as low as 15.5 mW/(m K). Compared to the CNF aerogel, increasing emulsion content can lead to better volume retention with significantly reduced density (11.4 mg/cm 3 ), increased mesoporosity, and enhanced specific modulus (18.2 kPa/(mg/cm 3 )) and specific yield strength (1.6 kPa/(mg/cm 3 )). In addition, the CNF/emulsion composite aerogel also demonstrates superb flexibility and infrared shielding performance.

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The widespread utilization of cellulose nanofibril (CNF) has been significantly hindered by its inherent flammability. To explore the potential of using CNF aerogel as sustainable material with good fire‐retardant and thermal‐insulating properties, CNF aerogel is modified by in situ supramolecular assembly of melamine (MEL) and phytic acid (PA). This strategy addresses CNF's flammability and avoids the environment issues associated with the incorporation of traditional fire‐retardant. The modified aerogel exhibits highly porous honeycomb structure with low density and good mechanical properties. After modification with MEL–PA, the aerogel exhibits highly improved shape integrity during burning, higher thermal stability, and favorable combustion behavior for fire retardancy. The heat transfer of the modified aerogel is well hindered, which demonstrated effective thermal insulation performance. In view of the excellent thermal and fire‐retardant properties, the MEL–PA/CNF composite aerogel can be a potential fire‐retardant and thermal‐insulating material for applications such as clothing, building, and electronic devices.

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