Fully Plant‐Based and Optically Transparent Wood Substrates with Improved Thermal Insulating Properties

Abstract Transparent wood composites are gaining interest for their superior properties over natural wood (PW), including superior transparency, thermal insulation, and stability. These composites are manufactured via infiltration of bio‐based polymers into porous bleached wood (BW), offering a sustainable alternative to glass and plastic in applications such as energy‐efficient windows and smartphone displays. In this study, the highest level of transparency in transparent wood (TW) substrates is achieved using biobased resins and an environmentally friendly bleaching process. Pristine balsa wood is bleached using non‐toxic chemicals and subsequently infiltrated with two bio‐based commercial resins, both sustainable and biocompatible. The performance of these bio‐based composites is compared to conventional epoxy resin. Resin viscosity is shown to influence the physical, optical, thermal, and mechanical characteristics of the final composite due to its ability to penetrate and interact with the wood's porous structure. Notably, the plant‐based soya resin‐infiltrated TW achieves exceptional properties, as 91% transparency at 550 nm, alongside remarkable UV stability and hydrophobicity. Additionally, this bio‐based composite shows a ≈50% reduction in thermal conductivity compared to standard glass (≈1 W m·K ⁻¹ ), highlighting its potential as a thermally insulative, energy‐efficient material for building‐integrated applications.