Paper-based packaging materials have gained attention from academia and industry for their outstanding environmental sustainability advantages. However, they still encounter major challenges, such as low mechanical strength and inadequate functionality, hindering the replacement of unsustainable packaging materials. Inspired by the remarkable strength of trees provided by cellulose fibers and the water and heat protection of trees provided by bark, this study developed a new biomass-based packaging material (SNC-C) that combines strength, thermal insulation, and water resistance. The material was created by simply blending straw nanocellulose (SNC) with oak bark (i.e., cork), which naturally provides water-resistant, thermal insulation, and unique regenerative properties. The dense layered structure formed entirely by SNC generates a tensile strength reaching up to 60.93 MPa. With the cork cavity structure, the heat transfer rate of the obtained material is reduced to 2.90–3.01 °C/(cm·min). The combining of the closed-cell structure and the suberin component of the cork results in a low water vapor transmission rate (WVTR) of the material of 400.30 g/(m²·24 h). This all-biomass material with excellent performance and low environmental footprint offers a promising solution for the development of sustainable multifunctional packaging materials.

The persistence of petrochemical plastics necessitates high-performance and recyclable alternatives, yet balancing mechanical robustness with component-level closed-loop recovery remains challenging for biomass-based plastic-replacement films. Here, a high-performance, thermo-malleable, and closed-loop recyclable composite film is constructed by integrating a highly crystalline enzyme-treated mulberry paper (Enzyme-MP) fiber network with an in situ formed polyimine (PI) vitrimer network via capillary-assisted infiltration. This process induces densification and extensive interfacial hydrogen bonding, forming a confined interpenetrating architecture that enhances stress transfer and restricts chain mobility. As a result, the composite film achieves a tensile strength of 70.3 MPa and a Young’s modulus of 2.37 GPa, together with excellent thermomechanical stability over a broad temperature range. The dynamic imine exchange enables thermo-malleability, allowing seamless self-welding and thickness-scalable lamination at 120 °C. The dense structure also acts as an effective barrier, reducing water uptake to 14.3% and providing resistance to various organic solvents. Furthermore, full-component closed-loop recycling is realized via room-temperature transimination, enabling selective depolymerization of the matrix while preserving the crystalline cellulose fiber network. This work demonstrates a viable strategy to integrate high-strength film performance, processability, and chemical recyclability in biomass-based composite films, while providing a basis for future cradle-to-cradle material circulation in recyclable plastic-replacement films.