Short, honest answers to the things people most often ask about vacuum insulated glazing. Want more depth? Every answer links through to a fuller guide.
It is a sealed glazing unit made of two panes of glass held a fraction of a millimetre apart by an array of tiny support pillars, with the gap between them emptied to a near-perfect vacuum and the edge sealed airtight. Because heat struggles to cross a vacuum, the unit insulates as well as much thicker double or triple glazing while being only about 6–8 mm thick.
No. Slim double glazing still has a thin cavity — usually 10–18 mm overall — filled with air or gas. Vacuum glazing replaces that cavity with a vacuum only a fraction of a millimetre wide, which is why it can be slimmer still and why it does not rely on a gas fill that can slowly leak away.
Once the air is removed, normal atmospheric pressure pushes the two panes together with a force of around 10 tonnes per square metre. Without support they would simply clamp shut. A grid of microscopic pillars — roughly 0.3–0.5 mm across, on about a 20 mm grid — holds the panes apart. They are barely visible at arm’s length.
Up close you can pick out the faint regular grid of pillars, and on some products a small sealed pump-out port in one corner. At normal viewing distance both are unobtrusive. AGC Fineo has no visible port; LandVac uses an unusually low pillar density; Pilkington Spacia has a visible port and a denser grid.
It depends on the product. The original frit-sealed Pilkington Spacia is about 1.1 W/m²K at the centre of the glass — as good as a modern double-glazed unit, but far slimmer. Newer tempered vacuum glass such as LandVac reaches 0.4–0.48 W/m²K, rivalling or beating triple glazing. For comparison, single glazing is about 5.7 and modern double glazing 1.2–1.6.
The best tempered and hybrid vacuum units match or beat triple glazing on U-value — in roughly a quarter of the thickness and at a fraction of the weight. Classic Spacia sits closer to good double glazing. The headline advantage of vacuum glass is not just the number but achieving it in a single-glazing profile.
It strongly resists condensation on the inside pane, because the vacuum keeps that pane close to room temperature even when it is cold outside. Condensation can still appear elsewhere — for example on cold external surfaces, or where a room is poorly ventilated — but internal misting is much less likely than with single or older double glazing.
Yes. Sound, like heat, does not travel through a vacuum, so vacuum glass gives a useful acoustic improvement over a single pane of the same thickness — around 35 dB for a standard unit and up to roughly 39 dB for laminated or tempered builds.
As a rough rule of thumb, vacuum glass runs around two to four times the price of standard double glazing at the glass level, though the gap narrows against triple glazing. Any specific figure is an indicative market estimate, not a quote — the real cost depends on size, product, whether it is toughened, and the joinery and installation. Always get itemised written quotes.
Lead times vary by product: AGC Fineo is usually quickest at around 4–8 weeks, LandVac longer at roughly 10–16 weeks (shipping from China), and Pilkington Spacia around 16 weeks. Heritage joinery work adds its own timeline on top.
Anyone can specify it. It simply tends to be chosen where its slim profile and appearance matter most — period and listed homes — because for a standard replacement window, conventional double glazing is usually cheaper and appearance is rarely constrained.
All three mainstream products are available in the UK. Fineo is made in Belgium (distributed here by Energlaze UK), LandVac in China, and Spacia in Japan. They are typically installed by heritage sash-and-casement specialists rather than high-street glaziers.
Often, yes — its ~6–8 mm profile fits frames cut for single glazing, so original windows can be kept. But altering windows in a listed building normally needs Listed Building Consent, and it is decided case by case. Historic England guidance suggests it is usually acceptable where there is no historic glass of interest, no leaded lights, and the glazing bars are substantial enough — and unlikely to be accepted where those conditions are not met.
No — and be wary of marketing that says so. Historic England publishes guidance on when slim and vacuum glazing can be acceptable; it does not formally approve or endorse specific commercial products. The decision on any particular window rests with your local planning authority’s conservation officer.
Comfortably. In England, Approved Document L requires a replacement window in an existing home to reach a U-value no worse than 1.4 W/m²K, or a Window Energy Rating of Band B. Vacuum glazing clears this easily.
Because EN 1279 — the standard for conventional double glazing — explicitly excludes vacuum glass. VIG has its own international standard, ISO 19916. So a vacuum unit is assessed against ISO 19916, not EN 1279; that is the correct standard, not a shortcoming.
Manufacturers claim vacuum retention of 25 years and upwards, with some figures of 60 years, and a getter inside the unit helps keep the vacuum stable by absorbing stray gas. These are manufacturer claims; independent long-term data at scale is still building, as the technology is relatively young. Warranties typically run 10–20 years.
Like any glazing it can fail, and the specific risk for vacuum glass is thermal stress — a large temperature difference across the panes. This is more of a concern for rigid frit-sealed units than for flexible-sealed tempered ones, which absorb the movement better. If the seal fails and the vacuum is lost, the unit’s insulation drops and it would need replacing.
Not always. The original Pilkington Spacia is annealed and needs an applied safety film where safety glass is required. Tempered products such as LandVac and HaanGlas are fully toughened safety glass in their own right, and units can also be laminated for safety and extra acoustics.
