How is transparent wood made, and what could it be used for?

Why transparent wood matters

Researchers have found ways to treat wood so that a thin sheet lets much of the light through while keeping its wood-like cell structure (Li and colleagues, 2016). A see-through version could in principle offer a plant-based alternative to some glazing and panel products. The sources describe laboratory samples, and the gap between a small clear sample and a useful product is large, as the limits below show.

How it is made

Lignin, one of the main components of wood, contains light-absorbing groups called chromophores, so researchers either remove the lignin or bleach those groups (Pugliese and Malucelli, 2025). The porous, cellulose-based scaffold that remains is the starting point for the next step.

Some methods bleach rather than remove. A 2021 approach from a University of Maryland group, reported in Physics Today, brushes hydrogen peroxide onto the surface and exposes it to ultraviolet light. This removes the light-absorbing chromophores of lignin while keeping some of the lignin itself (Wilson, Physics Today, 2021).

The pores are then filled with a clear polymer. The key condition is refractive index matching. The 2025 review by Pugliese and Malucelli says the key point is a match between the refractive index of the treated wood and that of the infiltrated resin, and identifies refractive index mismatch as the dominant source of haze (Pugliese and Malucelli, 2025). In the 2016 study by Li and colleagues, the wood was filled with refractive-index-matched, prepolymerised methyl methacrylate, which forms the plastic PMMA (Li and colleagues, 2016).

What has been demonstrated

The figures in this section are measured values reported in the abstracts of peer-reviewed papers. Each one depends on the sample, so they should not be read as a single property of the material.

Li and colleagues reported transparent wood with transmittance as high as 85% and haze of 71%. They said its optical properties could be tuned by changing the cellulose volume fraction. Their abstract mentions a synergy between wood and PMMA in mechanical properties but gives no strength figures (Li and colleagues, 2016).

Zhu and colleagues reported two types of highly anisotropic, highly transparent wood composites, with total transmittance up to 90%. Their abstract says the two types have very different optical and mechanical properties, but gives no further figures (Zhu and colleagues, 2016).

Two gaps remain in this evidence. Neither abstract gives measured strength or thermal values. The strength and thermal figures below come from press coverage or from the review's summaries of other studies, and none of the sources describes a building-scale insulation test.

What is only reported

Several figures come from press coverage or from a review summarising other studies. We have not checked them against the primary papers.

The Physics Today report describes transmittance up to 90% across 400 to 800 nm for the peroxide and ultraviolet method, with an epoxy polymer filled in afterwards. The article shows a 1 mm thick balsa sample but does not state the thickness behind the 90% figure. It gives a tensile strength of 20.6 MPa for the lignin-modified wood, against 0.4 MPa for wood with lignin fully removed by the conventional method. The Physics Today writer describes the process as "fast, scalable, inexpensive, and environmentally friendly"; the article gives no cost or environmental data to support this (Wilson, Physics Today, 2021).

The 2025 review also summarises bamboo studies by other groups. In one study by Wang and colleagues, a 1.5 mm Moso bamboo sample reached 87% transmittance and 90% haze, with tensile strength of about 118 MPa and thermal conductivity of about 0.33 W per metre-kelvin. In a separate study, also by Wang and colleagues, 1 mm samples reached 80% transmittance and 72% haze, and the method was reported to produce sheets up to 15 cm wide (Pugliese and Malucelli, 2025). These numbers come from the review's summary and are not verified here.

The KTH research page says filling the wood with polymer makes the material stiffer and stronger, as well as transparent. The page gives no test data for this claim (KTH).

What is speculative

The following uses have been proposed, but the sources do not test them in real buildings or products.

• Windows and light-transmitting buildings. Li and colleagues describe lightweight, strong transparent wood as a potential candidate for low-cost, light-transmitting buildings and transparent solar cell windows (Li and colleagues, 2016).
• Other research directions. The KTH group's publication list includes papers on smart windows, passive radiative cooling and transparent wood substrates for perovskite solar cells. The page itself gives no performance results for any of these (KTH).
• Structural use at scale. The sources describe small and moderate-sized sheets. None shows a structural panel or load-bearing element in use.

Limits and open problems

• Processing chemicals. The review says lignin removal may use quite toxic products and produce environmentally harmful by-products such as sulfides and chlorinated compounds, which is one reason it suggests lignin modification may be preferable (Pugliese and Malucelli, 2025).
• Haze. The reported haze values are high: 71% in the PMMA study and 90% for one bamboo sample. High haze scatters light and blurs anything seen through the material. The review calls haze an intrinsic limitation of high-clarity transparent wood (Pugliese and Malucelli, 2025).
• Cost. None of the sources gives production or cost figures. The "inexpensive" and "low-cost" descriptions are not backed by cost data in these sources.
• Durability. The review describes long-term stability under environmental stress as "a critical bottleneck" for outdoor use. It also says few studies have measured how transmittance and haze change under long ultraviolet exposure, damp heat or temperature cycling (Pugliese and Malucelli, 2025).
• Scale. The review says optical quality often deteriorates when samples are scaled up to large areas or multi-millimetre thicknesses, although in one balsa study larger 200 by 100 by 1 mm samples performed similarly to small ones. It also notes the absence of standardised protocols for measuring transmittance and haze (Pugliese and Malucelli, 2025).
• Comparison with glass. None of the sources compares transparent wood with glass on strength, durability or price, so no direct claim can be made here.

What to watch next

Useful signs of progress would be haze reported at the thicknesses used in windows and panels, measured with a shared test method. Outdoor ageing data under ultraviolet light, humidity and freeze-thaw cycles, which the review says are needed, would also matter (Pugliese and Malucelli, 2025). Finally, the primary papers behind the Physics Today figures, and larger sheets with transmittance and haze reported together, would show whether the early results hold up.