Toward the optimization of the optical behavior of transparent wood: current state of the art and perspectives

Transparent wood (TW) is a type of bio-based optical composite that combines wood’s hierarchical microstructure with polymers’ tailored optical properties to achieve high transmittance and controlled light scattering. TW is developed by removing lignin or modifying lignin chromophores and infiltrating a polymer whose refractive index closely matches that of the delignified wood framework. This review critically examines the parameters governing transparency in millimeter-thick TW, including the influence of wood species, delignification and bleaching strategies, and polymer selection for infiltration and polymerization/curing. The discussion emphasizes the interplay between microstructural anisotropy, refractive index matching, and processing-induced defects, which collectively determine light transmittance and haze. The review summarizes current progress toward achieving glass-like transparency in the millimeter range, highlighting the advances and remaining challenges in optimizing TW for scalable structural and functional applications.