Transparent wood in construction, from engineered material to smart building applications
What if future buildings were made entirely of wood, including windows and glazed surfaces? The idea is less far-fetched than it may sound. For several years now, transparent wood has been gaining attention in the field of engineered materials, opening new possibilities for architecture and construction.
Transparent wood is created by chemically treating natural wood to increase its optical transmittance, giving it properties that traditional timber does not possess. First developed in 2016 at the KTH Royal Institute of Technology in Sweden, this biomaterial has since been the subject of continuous research. Over time, it has gained additional functions, including the ability to absorb, store, and release heat, making it particularly attractive for energy-efficient buildings.
Passive smart windows made from transparent wood
The latest advances come from South Korea, where researchers have used this biocomposite to develop an innovative passive smart window. Unlike conventional smart glazing systems, this window can regulate the transmission of visible light based on temperature, without any external energy input.
A research team from Kongju National University and Hanbat National University developed thermochromic transparent wood using liquid crystals, a first for this type of material. To understand the significance of the breakthrough, it helps to look at the limitations of existing smart window technologies.
Limits and advantages of PDLC liquid crystals in smart technologies
Polymer-dispersed liquid crystals (PDLC) are smart materials that can switch between opaque and transparent states depending on temperature, allowing control over light and heat transmission.
One of the main drawbacks of PDLC systems is their limited ability to block and modulate ultraviolet radiation. While composite thin films can be added to filter UV rays, these solutions tend to be fragile and costly, reducing their practical appeal for large-scale building applications.
Technical performance and insulation of transparent balsa wood
The South Korean researchers addressed these issues by developing a new form of transparent wood tailored specifically for smart window use. They chemically treated balsa, basswood, and pine to remove lignin, which is responsible for wood’s natural dark color, effectively whitening the material. The resulting porous structure was then filled with a mixture of thermochromic liquid crystals and optical adhesives.
Balsa wood delivered the best results. It showed a progressive change in transmittance as temperatures increased, shifting from an opaque state with 28 percent transmittance at room temperature to a transparent state with 78 percent transmittance at 40 °C, measured at 550 nm. This behavior enables fully autonomous light regulation without any energy consumption.
The material also blocks nearly 100 percent of ultraviolet radiation and has a thermal conductivity of 0.197 W/m/K. In practical terms, this makes it almost five times more insulating than conventional glass, reinforcing the potential of transparent wood in construction as a high-performance alternative to traditional glazing.
Future applications, from sustainable buildings to wearable devices
“Our innovation is a direct and environmentally friendly substitute for glass. It provides privacy at night and natural daylight during the day, while reducing the energy demand of heating, ventilation, and air conditioning systems,” said Professor Jin Kim, who led the research team. “It is also ideal for smart greenhouses, as it prevents crop damage by automatically regulating sunlight and maintaining stable internal growing temperatures.”
Beyond building applications, the researchers see potential in wearable technology. The material could be used as a flexible patch that becomes transparent when body temperature exceeds 38 °C, offering an immediate visual health alert without the need for batteries or electronic components.
The study, titled Polymer dispersed liquid crystals-impregnated switchable thermochromic transparent woods with excellent ultraviolet blocking performance for smart windows, was published in the journal Advanced Composites and Hybrid Materials in 2025. DOI: 10.1007/s42114-025-01481-0