Double glazing for timber windows
This is the long read on the glass we fit into original timber windows across Victoria and Tasmania. It covers how vacuum glass works, what the three Glavenir specifications measure, how vacuum glass compares with the other two glass options we install, what the independent research says, and where to read more from Panasonic, VIGA and our own articles.
Request a quote See the numbersThe technology
Ordinary double glazing slows heat down by trapping a thick layer of air or argon between two panes. Vacuum insulated glass takes a different approach. Two panes of glass sit a tenth of a millimetre apart and the air between them is pumped out, leaving a vacuum. With almost no gas left in the gap there is very little to carry heat from one pane to the other, which is the same idea that keeps a vacuum flask hot all day.
Because the gap is so thin, the finished unit is only 6.1mm or 8.1mm thick. That is why it beds into the original rebate of a timber sash where a 20mm to 28mm double glazed unit never could.
Air pressure pushes the two panes together with a force of about ten tonnes on every square metre of glass. A grid of tiny ceramic pillars, roughly half a millimetre across, holds the panes apart at a fixed distance. Panasonic puts the load on each pillar at around 200 megapascals, about 2,000 times normal atmospheric pressure. You can see them as faint dots if you look for them, and most people stop noticing within a week. More on the pillars, on the VIGA site.
The perimeter is sealed with a solid lead-free glass seal rather than the rubber spacer and desiccant used in a conventional double glazed unit. There is no rubber to perish, no argon to leak out and no drying agent to saturate. The seal grew out of the technology Panasonic developed for plasma display panels, which is why the annealed unit has no evacuation hole at all and the toughened unit’s port sits flush with the surface.
A small sorption getter set into the edge of the unit absorbs any stray gas molecules released by the glass over the years, so the vacuum stays stable. The inner pane also carries a low-E coating that reflects radiant heat back into the room. Conduction, convection and radiation are the three ways heat crosses a window, and this construction closes all three. More on the getter, on the VIGA site.
Read more: What’s a vacuum and what are the black dots? · What is the sorption getter in vacuum glass? · What your vacuum glass installation will actually look like · The great black dot panic
Glavenir by Panasonic
Sealasash installs three configurations of Glavenir. All three share the same vacuum construction and the same 10mm minimum rebate depth, so the choice comes down to how much daylight and winter sun you want, and whether the window needs Grade A safety glass.
| Specification | 6.1mm Thermal (annealed) | 6.1mm Superclear (annealed) | 8.1mm Superclear (toughened) |
|---|---|---|---|
| Make-up | Low-E 3mm + 0.1mm vacuum + 3mm float | Low-E 3mm + 0.1mm vacuum + 3mm float | Low-E 4mm toughened + 0.1mm vacuum + 4mm toughened |
| U-value (W/m²K) | 0.7 | 0.9 | 0.58 |
| Visible light transmission | 75% | 79% | 81% |
| Solar heat gain (SHGC) | 0.39 | 0.57 | 0.52 |
| Sound reduction Rw (C;Ctr) | 35 dB (-2;-5) | 35 dB (-2;-5) | 36 dB (-2;-5) |
| Pillar spacing | 20mm | 20mm | 40mm |
| Evacuation port | None | None | Yes, flat, 10mm diameter |
| Grade A safety glass | No | No | Yes, tested in Australia to AS 2208 |
| Pane sizes | 150 x 150mm up to 1300 x 2300mm | 150 x 150mm up to 1300 x 2300mm | 200 x 500mm up to 1600 x 2540mm |
| Bushfire rating (new windows) | BAL Low | BAL Low | BAL 12.5 |
| Best suited to | The coldest rooms and south-facing windows, where warmth matters most | Living areas where you want more daylight and winter sun through the glass | Doors, low sills and any window where the code calls for safety glass |
| Warranty | 10 years by Panasonic, plus a further 5 years underwritten by Sealasash (15 years in total), installed to AS 1288 | 10 years by Panasonic, plus a further 5 years underwritten by Sealasash (15 years in total), installed to AS 1288 | 10 years by Panasonic, plus a further 5 years underwritten by Sealasash (15 years in total), installed to AS 1288 |
U-value and SHGC are centre-of-glass values to ISO 9050 (JIS R3106-1998) from Panasonic’s measurements and are not guaranteed values. Source: VIGA comparison table (May 2025) and Panasonic’s Glavenir product page.
You will see vacuum glass described as both 8.5 times and 10 times better than old glass. Both are right for their configuration. Panasonic compares its 6.1mm unit at 0.7 with a single 3mm to 6mm pane at 5.9 to 6.0, which is about 8.5 times. The 8.1mm toughened unit at 0.58 against 3mm glass at 5.7 is about 10 times. Against a 36mm triple glazed unit at 0.8, the 6.1mm Thermal unit is about 12% better and the 8.1mm unit about 27% better.
Thermal is our default for bedrooms and the cold side of the house. Superclear suits north-facing living rooms where you want the winter sun to do some of the heating. The toughened 8.1mm unit goes into doors, sidelights and windows with low sills, where Grade A safety glass is required. Most homes end up with a mix, and we set that out room by room in the quotation.
Downloads: Panasonic Glavenir spec sheet (PDF) · VIGA detailed comparison table (PDF) · Sealasash Glavenir aftercare guide (PDF) · Glavenir overview page
Choosing your glass
Vacuum glass is the top of our range, but it is not the only way to improve a timber window. We also reglaze with two Viridian products, EnergyTech single glazing and ComfortPlus laminated glazing. The comparison below uses each manufacturer’s published figures. The baseline is the thin 3mm glass most period windows still carry.
| Old 3mm glass | EnergyTech Clear 4mm | ComfortPlus Clear 6.38mm | Glavenir 6.1mm Thermal | Glavenir 8.1mm toughened | |
|---|---|---|---|---|---|
| What it is | Single pane, no coating | Single pane with a hard-coat low-E surface (Viridian) | Two panes laminated with a low-E coating (Viridian) | Two panes with a vacuum between them (Panasonic) | Two toughened panes with a vacuum between them (Panasonic) |
| Thickness | 3mm | 4mm | 6.38mm | 6.1mm | 8.1mm |
| U-value (W/m²K) | 5.9 to 6.0 | 3.7 | 3.6 | 0.7 | 0.58 |
| Heat loss through the glass compared with old 3mm glass | Baseline | About 38% less | About 40% less | About 88% less | About 90% less |
| Visible light transmission | About 90% | 83% | 82% | 75% | 81% |
| Solar heat gain (SHGC) | 0.87 | 0.72 | 0.69 | 0.39 | 0.52 |
| Sound reduction (Rw) | About 29 dB | ~29 dB | About 33 dB, typical for 6.38mm laminated glass | 35 dB | 36 dB |
| Safety glass | No | Grade A when toughened | Grade A laminate | No (annealed) | Grade A, AS 2208 |
| Fits the original rebate | Yes | Yes | Yes | Yes, 10mm rebate | Yes, 10mm rebate |
| Position in our range | What you have now | Entry level | Mid range, quieter | Premium | Premium, safety rated |
| Budget guide | $ | $$ | $$$ | $$$ |
Viridian figures are from its published product data (LBL Window 7, NFRC 100-2010 conditions). Glavenir figures are to ISO 9050. The two methods are close but not identical, so treat differences of a few percent between brands as noise. Percentages use Panasonic’s single-pane baseline of 6.0 W/m²K. Old-glass light, solar gain and sound figures are from the Sealasash Glavenir specification sheet.
Every one of these options is fitted together with our draught and acoustic seals, because new glass in a rattling sash is money wasted. Most of the heat and noise in a sash window slips around the pane through the operating gaps, not through the glass. The reglaze also starts with a full overhaul of the window, so cords, pulleys, sills and joints are sorted before the new glass goes in. See what a good retrofit looks like.
A low SHGC keeps summer heat out but also blocks some of the free winter warmth from the sun. In Hobart and Melbourne that is a trade-off worth thinking about window by window, which is why we offer Glavenir Superclear alongside Thermal. Our article on solar heat gain walks through it.
Manufacturer pages: Viridian EnergyTech · Viridian ComfortPlus · Panasonic Glavenir · Our double glazing page
Noise in real life
The Rw figures above come from laboratory tests of the glass on its own. To find out what Glavenir does in a real house, VIGA fitted it to a home in Geilston Bay that faces the East Derwent Highway, one of Hobart’s busiest roads, and had NVC, an independent acoustic consultancy, run in-situ sound isolation testing in February 2025.
The 8.1mm toughened Glavenir, on its own, achieved a DnT,w of 43 dB. DnT,w is the weighted standardised level difference between the noise outside and the noise inside a finished room, frame and all, so it reflects what you hear rather than what a test rig measures. NVC’s report puts that 8.1mm pane on a par with a conventional double glazed unit made from two 8.5mm VLam Hush acoustic laminates with a 12mm air gap, a unit roughly 29mm thick.
Read the full write-up on the VIGA site · Soundproofing with glass · The quiet truth about sash windows
In plain terms
When it is 0°C outside and 20°C inside, the room side of old single glazing sits at around 6°C. High-performance glass such as Glavenir keeps that surface at 17 to 19°C, so the window stops pulling heat out of the room. An easy way to understand glass performance
Condensation forms where warm indoor air meets a cold surface. Keep the glass warm and the weeping windows, black mould on the sill and lifting paint largely stop. Can vacuum glass stop condensation and mould?
The vacuum layer is a poor carrier of sound as well as heat. Glavenir is rated Rw 35 to 36 dB, which Panasonic’s testing puts about 18% ahead of a standard double glazed unit, once the frame gaps are sealed. In a real Hobart home beside the East Derwent Highway, the 8.1mm unit measured a DnT,w of 43 dB. Noise in real life
A 6.1mm unit weighs about the same as 6mm of plain glass, roughly 15 kilograms per square metre. A triple glazed unit with three 4mm panes weighs twice that, which is why triple glazing was never a serious option for a sash hung on cords and weights.
Because the unit is barely thicker than the glass it replaces, it beds into the existing rebate. Putty lines, glazing bars, arched sashes and heritage profiles are all retained. Can you keep the original frames?
The Australian Government’s YourHome guide puts window heat loss at up to 40% of a home’s heating energy, and Sustainability Victoria notes that a single pane can lose almost ten times as much heat as the same area of insulated wall. YourHome on glazing · Where your home really loses its heat
From our Google reviews in Tasmania and Victoria
“I have recently upgraded my previously rejuvenated sash windows upgraded to the Glavenir glass from Panasonic by the Sealasash team. The result is nothing short of amazing. The installation team led by Scott were extremely professional and it all went seamlessly. The thermal and acoustic results are everything and more than what I was hoping for. I can thoroughly recommend this product and the entire Sealasash team.”
John Mills, Battery Point, Tasmania. Via Google Reviews
“We got our sash windows on a 1900s weatherboard upgraded to Glavenir vacuum glass, its amazing. Quieter and less heat transfer than some double glazed windows we have also, and we kept the original sashes. The guys put in draught seals on windows and doors which have made a big difference too. Everything ran smoothly, to schedule and budget. Excellent work and excellent product. Thanks Scott, Jack and the crew!”
Davo A, West Hobart, Tasmania. Via Google Reviews
“We recently had our windows refurbished and fitted with Glavenir Vacuum Insulated Glass. We were very impressed with the efficient way in which the Sealasash team implemented the installation process. The vacuum glass has made an absolutely incredible difference to our home, improving the performance both thermally and acoustically beyond our expectations!”
Kate Symonds, New Town, Tasmania. Via Google Reviews
“Andrew and the team were quick, polite and thorough in replacing the glazing of sash windows in my early Victorian cottage in St Kilda. The windows slide better than ever and the Glavenir glazing product has specs equivalent to triple glazing I understand. Can’t wait to experience a toasty winter with less energy usage. The house was left mess free.”
Tim Issacson, St Kilda, Victoria. Via Google Reviews
“We recently had Sealasash restore the original timber sash windows in our Victorian home, and we are beyond impressed with their work. […] One of the highlights of the service was the Glavenir glass. This energy-efficient, high-performance glazing not only retains the traditional look of my windows but also provides incredible thermal and acoustic insulation. Since the installation, my home has been quieter, warmer, and much more energy-efficient. For example, last week I measured the outside vs inside glass temperature… 7.6deg outside vs 17.8deg inside.”
Kate Kennedy, Melbourne, Victoria. Via Google Reviews
“I am more than happy with the outcome of my new windows from Seal-a-Sash. A great experience from the team and more than happy to recommend the Panasonic Glavenir double glazed product. My experience has been excellent.”
Craig Ryan, Windsor, Victoria. Via Google Reviews
Independent science
Vacuum insulated glazing was invented at the University of Sydney. Richard Collins and Stephen Robinson published the first working design in the journal Solar Energy in 1991, and the university’s School of Physics has stayed at the centre of the field ever since. Dr Cenk Kocer, a senior researcher there with more than three decades in glass mechanics and thermal testing, is among the most cited authors on how vacuum glass performs and why it lasts. His work is independent of Panasonic and of Sealasash, which is exactly why we point to it.
Kocer’s 2019 review describes the working recipe: a gap of about a tenth of a millimetre, a pressure of 0.1 pascal or lower, an array of high-strength spacers, and a hermetic edge seal designed to hold that vacuum over a service life of 25 years or more. Combined with a conventional cavity, he notes, the technology has a practical floor of around 0.2 W/m²K.
His 2025 paper with Antti Aronen and Christian Alter sets out how each half-millimetre pillar acts as a small thermal bridge and a point of very high contact pressure, and how pillar size, shape and material decide the outcome. It is the reason Panasonic’s pillar material and spacing matter more than their colour.
Two 2023 papers in Glass Structures and Engineering show that heat concentrates at the pillars, so common laboratory instruments can misread a vacuum unit’s insulation unless the method allows for it. It is why we quote U-values together with the standard they were measured under.
Aronen and Kocer modelled what happens when one face of the unit is much warmer than the other. The rigid glass seal means the panes bend slightly and carry stress, which is designed for in the pane thickness and unit size. Those models were validated against measurement.
Work with Technische Universität Darmstadt modelled vacuum units under wind load for the low-rise residential windows most of us live behind, checked against European and North American codes, and tested how units behave when a soft body strikes them.
A 2025 life-cycle study weighs the energy embodied in making a vacuum unit, from raw materials to transport, against the energy it saves in a building over its life, and finds where the payback point sits. The international test standard for the product is ISO 19916.
Where the glass comes from
Panasonic entered the vacuum glass business in 2017, applying the precision glass handling, vacuum sealing and hermetic bonding it had perfected making plasma television panels. Its roughly 6mm unit at 0.7 W/m²K set the benchmark for thin vacuum glass. In 2019 production for European housing began with AGC Glass Europe, and in December that year Panasonic announced a toughened version made possible by a new super-low-temperature sealing material, and gave the product its name. Glavenir is a blend of glass and avenir, the French word for future.
The units are lead free, flat on both faces, and made in a range of clear and toughened configurations. The Australian retrofit market has been a focus since 2023, when Sealasash management was hosted at Panasonic’s headquarters in Osaka, and the only case study on Panasonic’s own Glavenir page is a Sealasash project in Tasmania.
Panasonic Glavenir product page · Panasonic press release, December 2019 · Fineo, the European sibling by AGC · Sealasash visits Panasonic HQ · From Japan to your wooden windows · From a plasma screen factory to your windows (VIGA)
Australia does not manufacture vacuum glass at this scale, so Sealasash went to the source. After trials with Glavenir, the company secured a supply agreement with Panasonic and set up VIGA, its national wholesale arm. VIGA imports genuine Glavenir and supplies it to glaziers, retrofit businesses and new window manufacturers across the country, through approved installers who fit it to AS 1288.
The VIGA site holds the detailed specifications, the installer network, project write-ups from other glaziers, and the notes from the annual review with Panasonic Housing Solutions in Japan.
vacglass.com.au · Glass specifications · FAQ · Approved installers · Projects · News · Back in Japan: annual review with Panasonic · Australian first: a house reglazed with Glavenir · 70 panes into a Melbourne high-rise
Keep reading
Every card below is a link. Click any of them to open the article or project.
Melbourne’s north-east, 767 sectionsSuperclear Glavenir and acoustic laminate across a whole home.See the project →
West Hobart, Melville StreetFixed sashes and Yorkshire sliders with 6.1mm Glavenir.See the project →
Shoreham coastal upgrade67 panes of Glavenir in a cedar home on the Mornington Peninsula.See the project →
Dodges Ferry52 panes of vacuum glass in cedar frames by the beach.See the project →
Hobart’s Eastern Shore8.1mm toughened Glavenir, comfort without compromise.See the project →
Hobart, a Tasmanian first28 panes, and a Panasonic representative flew in to see it.See the project →
Kew, Sir Robert Menzies’ former homeArched sashes and colonial bars retained.See the project →
New Town, Bob and ChristineFrom draught seals in 2014 to vacuum glass today.See the project →
All recent jobsBrowse every project across Victoria and Tasmania.Browse the projects →
Questions we’re asked
On centre-of-glass U-value, yes. Glavenir measures 0.7 and 0.58 against 0.8 for a 36mm triple glazed unit in Panasonic’s comparison to JIS A2102. It also lets more daylight through (75% to 81% against 71%) at a quarter of the thickness and about half the weight.
Yes, if you look for them, as a faint grid of dots about half a millimetre across. They blend into the view rather than the glass, and most owners tell us they stop noticing within the first week. Our article on the dots covers this in detail.
The seal is solid glass with no rubber and no gas to escape, and a getter absorbs any stray molecules over the years. The research community designs vacuum glazing for a service life of 25 years or more and VIGA quotes an expected life beyond 50 years. Panasonic backs each unit with a 10-year warranty and Sealasash underwrites a further 5 years on top, 15 years in total. Every pane carries an etched QR identifier for that warranty.
Usually, because the original sashes, profiles and glazing bars are retained. Draught sealing and reglazing within existing sashes are generally treated as minor works, but replacing early glass in a registered place may need a permit, and we work within that process. Read about heritage approval.
Glavenir Thermal for the coldest rooms, Superclear where daylight and winter sun matter, and the toughened 8.1mm unit for doors and low windows. EnergyTech or ComfortPlus where budget leads and a smaller improvement is enough. We set the mix out room by room in the quotation, and you can change it before the glass is ordered.
Yes. Most of the heat and noise in a sash window slips around the pane through the operating gaps, not through the glass. Seals are fitted as part of every reglaze so the new glass can do its job.
Tell us about your windows and which glass interests you. We provide a free quotation or price guide after you submit the enquiry form, and we work across Victoria and Tasmania.
Standards referenced on this page: AS 1288 (glass in buildings, installation), AS 2208 (safety glazing materials), ISO 9050 and JIS R3106 (light and solar characteristics of glazing), JIS A2102 (thermal performance of windows), ISO 19916 (vacuum insulating glass). Performance figures are manufacturers’ published centre-of-glass values and are not guaranteed values for a finished window.
