Thermo-reversible transparent wood with tunable optics and mechanics for energy-efficient windows

Transparent wood (TW) has emerged as a promising alternative to glass for sustainable architecture, yet its rigid and passive nature limits its adaptability for dynamic light and temperature regulation. We report a thermally reversible transparent wood (TRTW) featuring a semi-interpenetrating polymer network architecture constructed from polyethylene glycol (PEG) and poly (ethylene glycol) diacrylate (PEGDA) infused into a delignified wood scaffold. This architecture enables reversible transitions between stiff and soft states via PEG crystallization/melting and dynamically modulates light transmittance (from 80.6% to 48.2%) through refractive index mismatch. The TRTW exhibits excellent shape adaptability at elevated temperatures (bendability exceeding 170°), enhanced toughness (elongation increased by 540%), and superior impact resistance (9.81 kJ/m2, ~ 12× that of glass). It also features an adjustable phase transition temperature (Tm ≈ 30 °C, Tc = 12.96–18.85 °C) and high latent heat (up to 95.8 J/g), enabling heat storage and temperature buffering for passive building energy regulation. The synergy of thermo-reversible optics and mechanics within a wood-based framework provides a novel strategy toward intelligent and energy-efficient building skins and optical devices.