The Natural Blueprint of Wheat Straw Foam: Preserved Structure Enables Robust Mechanics and Thermal Insulation

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The growing demand for sustainable lightweight foams is constrained by the ecological challenges posed by their petroleum-based counterparts. Here, we present a novel approach utilizing wheat straw, an abundant yet undervalued agricultural residue with intrinsically oriented cellulose and a hollow architecture, through an “in situ delignification assembly” strategy. By preserving and utilizing the complete oriented hierarchical morphology of straw through delignification and poly(vinyl alcohol) (PVA) binding, we fabricate anisotropic delignified wheat straw/PVA foams (DWS/PVA) with programmable mechanics via controlled alignment of DWS units. The foams achieve a specific compressive modulus as high as 1133 MPa·g –1 ·cm 3, low and anisotropic thermal conductivity (94% porosity, 0.037 W·m –1 ·K –1 conductivity perpendicular to the fiber axis, anisotropy coefficient ∼1.7), and passive radiative cooling performance with a subambient cooling temperature drop of 4 °C. Crucially, the sustainability of the foam, characterized by its recyclability and biodegradability, positions it as a highly competitive alternative for disposable green packaging, energy-efficient buildings (cooling boards, exterior wall filling layers, etc.), and thermal management systems. Our structure-retaining design represents a pioneering approach in transforming cellulose-based waste into high-value functional materials.