Breaking the “Impossible Trinity” in Flexible Phase‐Change Materials with Dynamic Adaptable Encapsulation

The pursuit of flexible phase‐change materials (PCMs) for advanced thermal management is fundamentally constrained by a longstanding “impossible trinity”: achieving simultaneous high flexibility, high thermal conductivity, and large latent‐heat storage in a single material remains an unmet goal. Here, we break this paradigm via a “dynamic adaptable encapsulation” strategy. A double‐network skeleton of cellulose nanofibers (CNF) and aramid nanofibers (ANF), cross‐linked by reversible Fe 3+ ‑tannic acid (TA) coordination, is designed to create an adaptive matrix. This unique architecture concurrently provides dynamic stress dissipation​ for extreme stretchability (≈175% elongation), efficient phonon‐transfer pathways​ for rapid heat dissipation (3.50 W/(m·K)), and dense yet compliant confinement​ for preserving a high phase‐change enthalpy (>120 J/g). Molecular dynamics simulations reveal that the reversible metal‑phenolic bonds, which not only maintain strong interfacial adhesion but also percolate heat‐transfer networks under deformation, offering atomic‑scale insights into the synergy. Consequently, the composite film exhibits exceptional cyclic stability and reliable conformability to complex surfaces. Leveraging this synergistic foundation, the film demonstrates multifunctional capabilities, including efficient solar‐thermal conversion (94.59%) and effective electromagnetic interference shielding (≈30 dB), validated in multi‑scenario applications from flexible electronics cooling to high‑power device thermal regulation. This work establishes a generalizable design principle for adaptive thermal‐management materials.