An engineered transparent wood that can trap heat and then release it when needed could be the next trendy building material.
The new kind of wood not only transmits light, but is also able to absorb and release heat, potentially saving on energy costs.
Scientists say that the revolutionary material can bear heavy loads and is biodegradable, opening the door for its eventual use in 'eco-friendly' homes and other buildings.
"Back in 2016, we showed that transparent wood has excellent thermal-insulating properties compared with glass, combined with high optical transmittance," said Céline Montanari, a PhD student student at KTH Royal Institute of Technology in Sweden.
"In this work, we tried to reduce the building energy consumption even more by incorporating a material that can absorb, store and release heat."
As economic development progresses worldwide, energy consumption has soared. Much of this energy is used to light, heat and cool homes, offices and other buildings.
Glass windows can transmit light, helping to brighten and heat homes, but they don't store energy for use when the sun goes down.
To create the optically transparent wood, the researchers first removed a light-absorbing component called lignin from the cell walls of balsa wood.
To reduce light scattering, they incorporated acrylic into the porous wood scaffold.
The researchers could see through the material, yet it was hazy enough to provide privacy if used as a major building material.
The transparent wood also had favourable mechanical properties, enabling it to bear heavy loads.
Building on this work, Ms Montanari and lead investigator Professor Lars Berglund added a polymer called polyethylene glycol (PEG) to the de-lignified wood.
"We chose PEG because of its ability to store heat, but also because of its high affinity for wood," said Ms Montanari.
"In Stockholm, there's a really old ship called Vasa, and the scientists used PEG to stabilise the wood. So we knew that PEG can go really deep into the wood cells."
Known as a "phase-change material," PEG is a solid that melts at a temperature of 80 degrees fahrenheit (26.6 degrees centigrade), storing energy in the process.
The melting temperature can be adjusted by using different types of PEGs.
"During a sunny day, the material will absorb heat before it reaches the indoor space, and the indoors will be cooler than outside," said Ms Montanari.
"And at night, the reverse occurs - the PEG becomes solid and releases heat indoors so that you can maintain a constant temperature in the house."
Like their earlier version, the modified wood was transparent, though slightly hazy, and strong, but had the added bonus of storing heat.
The researchers say that the transparent wood has the potential to be more environmentally friendly than other building materials such as plastic, concrete and glass.
In addition to its thermal-storage capabilities, the researchers say that the transparent wood could be easier to dispose of after it has served its purpose.
"The PEG and wood are both bio-based and biodegradable," said Professor Beglund.
"The only part that is not biodegradable is the acrylic, but this could be replaced by another bio-based polymer."
The researchers estimate that transparent wood could be available for niche applications in interior design in as little as five years.
They are also trying to increase the storage capacity of the material to make it even more energy-efficient.
The research team were due to present their finding at the American Chemical Society (ACS) Spring meeting in Orlando, Florida.
