Windows and panels made of transparent wood

How far is transparent wood from use in windows and buildings?

Transparent wood is wood with its light-absorbing lignin removed and its pores filled with a clear polymer. Laboratory samples have reached about 90% light transmittance, but haze is often high and most samples are small lab pieces. A bio-based version has been reported in the lab with a strength figure. The sources reviewed give no pilot window or building installation, no cost figure, no building fire rating and no long-term outdoor test.

AI illustration · Illustrative scene, not a photograph of the specific device or experiment.
WHERE WE AREEngineering prototypes

Getting closer. Prototypes exist, but not in real-world use.

Lab samples have shown transmittance of up to about 90%, and a bio-based version has been reported with a strength of 174 MPa for a 1.2 mm sample. Lab prototypes exist, including a passive smart-window design reported in 2026. The sources reviewed show no pilot installation, no production route and no building-standard fire, cost or outdoor durability result, so the stage is engineering prototype rather than pilot.

The tech tree

Everything recorded on Vrulum that this future needs, oldest foundations at the top and the goal at the bottom. Lines show what each step requires.

What it takes: Windows and panels made of transparent wood Unlocked Being researched Locked
  1. 2016Transparent woodResearch and prototypes Being researched.
  1. 2016Transparent wood shown in the labDone Unlocked.
  2. 2021Bio-based polymer version shown in the labDone Unlocked.
  3. 2026Prototype smart window in the labDone Unlocked.
  4. Date not recordedHaze low enough for a clear viewIn progress Being researched.
  5. Date not recordedScale-up without loss of clarityIn progress Being researched.
  6. Date not recordedOutdoor durability shownIn progress Being researched.
  7. Date not recordedFire performance for building useNot started Locked.
  8. Date not recordedWhole-window heat and light testsNot started Locked.
  9. Date not recordedPilot installation in a buildingNot started Locked.
  1. GoalWindows and panels made of transparent woodGoalRequires: Transparent wood, Transparent wood shown in the lab, Bio-based polymer version shown in the lab, Haze low enough for a clear view, Scale-up without loss of clarity, Outdoor durability shown, Fire performance for building use, Prototype smart window in the lab, Whole-window heat and light tests, Pilot installation in a building. Locked.

The road so far

3 of 9 steps done, 3 in progress.

  1. Done · 4 Mar 2016Transparent wood shown in the lab

    Li and colleagues reported transparent wood made from a delignified nanoporous template filled with refractive-index-matched PMMA, with transmittance as high as 85% and haze of 71%. Zhu and colleagues reported total transmittance of up to 90% for two highly anisotropic composite types. Both are laboratory samples. [1][2]

  2. Done · 4 May 2021Bio-based polymer version shown in the lab

    KTH researchers reported a fully bio-based transparent wood, using a citrus-derived material in place of a fossil-based polymer. KTH's news release reports 90% transmittance, 30% haze, a strength of 174 MPa and elasticity of 17 GPa for a 1.2 mm sample. The release names the journal Advanced Science. The research paper was not opened, so these figures are reported, not verified. [3]

  3. In progressHaze low enough for a clear view

    Haze is still high. The lowest figures found are about 30% for a 1.2 mm bio-based sample (KTH news release, not verified against the paper) and below 36% for an optimised fir sample in the 2025 review. Many samples in the 2025 review have haze of 70% or more. [3][4]

  4. In progressScale-up without loss of clarity

    Balsa sheets of 200 by 100 by 1 mm have been reported, and the 2025 review says this scale-up did not affect optical properties. Bamboo sheets up to 15 cm wide have also been reported. The same review says optical quality often deteriorates when samples are scaled up to large-area or multi-millimetre specimens. The 2021 Physics Today report gives no production or scale-up cost data. [4][5]

  5. In progressOutdoor durability shown

    Some single tests exist. One study reports that dyed basswood shows less yellowing under UV than undyed samples, and one fir sample kept stable properties after 100 freeze-thaw cycles. The 2025 review calls long-term stability under UV, humidity and heat a critical bottleneck for outdoor use, and says few studies have quantitatively examined how transmittance and haze change under those stresses. [4]

  6. Not startedFire performance for building use

    Flame-retardant versions have been reported in lab studies. One balsa version, with a phosphate ester and polyethylene glycol treatment, reports a limiting oxygen index of up to 37% and self-extinction in a horizontal flame test. No fire test against a building product standard was found in the sources reviewed. [4]

  7. Done · 15 Jan 2026Prototype smart window in the lab

    A 2025 paper by researchers at Kongju and Hanbat National Universities, reported in a January 2026 article, describes a passive smart window made from treated balsa filled with thermochromic liquid crystals. Its visible light transmittance at 550 nm rises from 28% at room temperature to 78% at 40 °C. The article gives no sample size, durability, cost or fire performance for the window. [6]

  8. Not startedWhole-window heat and light tests

    The smart-window article reports a thermal conductivity of 0.197 W per metre-kelvin for the material. No whole-window heat-loss or solar heat gain test was found in the sources reviewed. [6]

  9. Not startedPilot installation in a building

    No pilot installation, manufacturer or price for a transparent wood window or panel was found in the sources reviewed. The KTH research page gives no pilot, partner or cost information. [4][7]

Why it matters

Windows and light-passing panels are common building parts. A bio-based option would matter only if it kept a clear view, lasted outdoors and met fire rules. None of these three points has yet been shown for transparent wood in a building.

What stands in the way

  • Haze. Many reported samples scatter so much light that a view through them would look cloudy. The lowest haze figures found, about 30% and below 36%, are still high.
  • Outdoor durability. Few studies have quantitatively examined how transmittance and haze change under UV light, humidity and heat.
  • Fire rating. Flame-retardant lab results exist, but no test against a building fire standard was found.
  • Scale-up. Optical quality often deteriorates in larger or thicker pieces, according to the 2025 review.
  • Measurement. The 2025 review says there is no universally accepted formal definition of haze, so results from different studies are hard to compare.
  • Cost. No production or price figures for transparent wood were found in the sources reviewed.
  • Chemistry. The 2025 review lists delignification routes that use alkaline hydrogen peroxide and acidified sodium chlorite at 60 to 90 °C. The environmental and safety effects of these routes at scale were not found in the sources reviewed.

Signals to watch

  • A transparent wood sheet at window size, with transmittance and haze measured to a published method and the thickness stated.
  • Ageing data showing how transmittance, haze and yellowing change after UV, humidity and heat exposure over a stated period.
  • A fire test result for a transparent wood panel against a building product standard.
  • A glazing or roofing pilot in a building, with measured light and heat performance published.
  • A disclosed price per square metre, or a manufacturer offering transparent wood panels.
  • A standard protocol for measuring transmittance and haze adopted by researchers or a standards body.

Sources

  1. peer reviewed paper
    Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance
    Li, Fu, Yu et al.. Biomacromolecules (ACS Publications), 4 Mar 2016.
  2. peer reviewed paper
    Highly Anisotropic, Highly Transparent Wood Composites
    Zhu, Song, Li et al.. Advanced Materials (Wiley), 4 May 2016.
  3. university press release
    Citrus derivative makes transparent wood 100 percent renewable
    KTH Royal Institute of Technology, 4 May 2021.
  4. review article
    Toward the Optimization of the Optical Behavior of Transparent Wood: Current State of the Art and Perspectives
    Diego Pugliese, Giulio Malucelli. Polymers (MDPI), 10 Dec 2025.
  5. news
    A fast, scalable approach to making wood transparent
    R. Mark Wilson. Physics Today (AIP Publishing), 1 Feb 2021.
  6. news
    The potential of transparent wood in construction
    Rinnovabili, 15 Jan 2026.
  7. other
    Transparent Wood
    KTH Royal Institute of Technology, Sept 2026.

Last reviewed 21 Oct 2026.