<p>Developing sustainable cellulose fibers foam that simultaneously provides thermal insulation and mechanical strength for energy-efficient buildings is crucial, but it is still challenging to realize. In this study, an interface-induced assembly strategy was employed to fabricate cellulose fibers composite foam, in which gas bubbles acted as dynamic templates and cationic bamboo powder mediated electrostatic coupling between cellulose fibers and sodium alginate at the bubble interface, thereby enhancing interfacial compatibility and foam structural integrity. Subsequent introduction of Ca²⁺ triggered ionic crosslinking in the alginate network, while in situ citric acid esterification further reinforced the structure. The foam utilizes the temporal coordination of multiple interfacial interactions to establish topological constraints within the fiber network, restricts chain segment mobility, achieves conformational locking, and significantly enhances skeletal stability. The thermal conductivity of the foam is as low as 0.046 W·m⁻¹·K⁻¹, which is comparable to that of commercial polystyrene foam (EPS). In addition, the compressive strength of the foam increases from 15.2 to 55.7 kPa, corresponding to an improvement of approximately 266%. This study proposes a fabrication strategy for cellulose fibers foam that eliminates petroleum-derived polymers. The foam simultaneously achieves low thermal conductivity and high mechanical strength, offering a promising and sustainable alternative for thermal insulation in energy-efficient buildings.</p> Graphical Abstract <p></p>