Vacuum glazing vs double glazing: a fair head-to-head
Ask whether vacuum glazing beats double glazing and the honest answer is more interesting than the marketing one. The original frit-sealed vacuum glass roughly matches a good modern double-glazed unit on insulation — but does it in the thickness of a single pane. The newest tempered vacuum glass goes further, edging into triple-glazing territory. So this is not a simple “newer is better” story. It is a comparison that turns on which vacuum unit you mean, and on what your window actually needs to do.
This guide sets the two technologies side by side on the things that matter in a British home: heat loss, thickness and sightlines, condensation, noise, appearance, durability and cost — and finishes with a plain “which should you choose, and when.”
What each one actually is
A conventional double-glazed unit, or IGU (insulated glass unit), is two panes separated by a sealed gap of roughly 12–20 mm. That gap is filled with a low-conductivity gas — usually argon — and at least one pane carries a low-emissivity (low-E) coating to reflect heat back indoors. Add the two panes and the whole sandwich is typically 24–28 mm thick. Triple glazing adds a third pane and a second gas gap, so it is thicker again — commonly around 40 mm or more.
Vacuum insulated glazing (VIG) attacks the same problem differently. Instead of slowing heat through a gas, it removes the gas altogether. Two panes are held about 0.1–0.2 mm apart by an almost invisible grid of tiny support pillars, the cavity is pumped down to a hard vacuum (on the order of 0.1 Pa), and the edge is hermetically sealed for life. Because a vacuum carries essentially no conduction or convection, that wafer-thin gap does the work of a much fatter gas-filled one. A complete VIG unit is only 6–8 mm thick — about the thickness of a single old pane. (Our main guide covers the underlying physics in more depth.)
That thickness difference — roughly a quarter of a double-glazed unit — is the headline, but it is not the whole comparison.
Thermal performance and the U-value ladder
Insulation is measured by U-value in watts per square metre per kelvin (W/m²K): the lower the number, the less heat escapes. It helps to keep two figures apart. Ug is the centre-of-glass value — the glass on its own. Uw is the whole-window value, which includes the frame and edge effects and is always a little higher (worse). Product data sheets usually quote Ug; building regulations care about Uw. Comparing a glass-only Ug to a whole-window Uw is one of the most common ways these numbers get muddled. Our U-values explained guide unpicks this properly.
Here is the centre-of-glass ladder, worst to best:
- Single glazing — around 5.7 W/m²K. The baseline for most pre-war windows.
- Old air-filled double glazing — roughly 2.8 W/m²K. Better, but dated.
- Modern low-E, argon-filled double glazing — about 1.2–1.6 W/m²K, with the best units near 1.1.
- Triple glazing — roughly 0.6–0.8 W/m²K.
- Best tempered vacuum glazing — down to about 0.4 W/m²K.
Now the honest part. The classic frit-sealed vacuum unit — Pilkington Spacia, the world’s first commercial VIG, launched in October 1997 — has a centre-of-glass U-value of about 1.1 W/m²K. That is genuinely good: it is level with a strong modern double-glazed unit. But it is not the sub-0.5 figure sometimes seen in marketing. Classic Spacia’s achievement is delivering double-glazing insulation in single-glazing thickness — not out-insulating double glazing.
Classic frit-sealed vacuum glass (≈1.1 W/m²K) is about equal to good modern double glazing on the U-value — its trick is doing it at a quarter of the thickness. Only tempered vacuum glass, such as LandVac at 0.4–0.48 W/m²K, actually beats double glazing outright.
The picture changed with tempered VIG. Low-temperature edge seals let the glass stay fully toughened and allow a sparser pillar grid, both of which cut heat loss. LandVac (from 2016) quotes 0.4–0.48 W/m²K; HaanGlas around 0.47–0.5 W/m²K; AGC’s Fineo is around 0.7 W/m²K. These figures land alongside — or below — triple glazing. And “hybrid” units, which bond a vacuum pane into a conventional gas-filled sealed unit, can reach 0.4–0.5 W/m²K with a whole extra pane’s worth of insulation; see triple, vacuum and hybrid glazing for how those stack up.
For context, England’s Approved Document L requires replacement windows in existing homes to meet a whole-window U-value of 1.4 W/m²K or better, or Window Energy Rating band B; new dwellings must hit 1.2. Both vacuum and modern double glazing clear these comfortably — so regulations are rarely the deciding factor between them.
| Modern double glazing | Triple glazing | Vacuum glazing (VIG) | |
|---|---|---|---|
| Centre-of-glass U (W/m²K) | ~1.2–1.6 (best ~1.1) | ~0.6–0.8 | 1.1 classic (Spacia); 0.4–0.7 tempered |
| Total thickness | ~24–28 mm | ~40 mm+ | ~6–8 mm |
| Relative weight | Moderate | Heaviest | Lightest (~20–28 kg/m²) |
| Acoustics (Rw) | ~29–32 dB typical | Varies with build-up | ~35 dB (Spacia) to ~39 dB (LandVac) |
| Fits a slim heritage frame? | No | No | Yes |
| Indicative relative cost | Baseline (1×) | ~1.5–2× | ~2–4× double glazing |
U-values are centre-of-glass Ug unless stated; thicknesses and costs are indicative market estimates, not quotes.
Thickness, weight and sightlines
This is where the two are least alike. A 24–28 mm double-glazed unit simply will not fit the rebate of a traditional single-glazed timber sash or slender steel casement without rebuilding or replacing the frame — and the deeper glazing bead and chunkier sightlines change how the window looks. A 6–8 mm vacuum unit drops into the same rebate as the original glass, so the frame, glazing bars and slim profiles can be kept.
It is lighter, too. A vacuum unit weighs roughly the mass of its two panes — around 20–28 kg/m² for an 8.3 mm build — noticeably less than a triple-glazed unit and gentler on old sash cords, weights and hinges. For contemporary joinery chasing minimal frames and maximum glass, that slimness is an aesthetic choice as much as a practical one. For a Georgian or Victorian window, it is often the only way to hit modern U-values without altering the character of the building. Our sash-window guide covers the retrofit detail.
Condensation and acoustics
Condensation resistance. Because the vacuum is such a good insulator, the indoor pane of a VIG stays close to room temperature even when it is bitterly cold outside. A warmer inner surface is far less likely to drop below the dew point, so vacuum glazing strongly resists the misting and running condensation that plague single glazing and tired old double glazing on cold mornings. Good modern double glazing resists interior condensation well too, but a warm-edge, low-U vacuum unit is among the most condensation-resistant options available — one reason it suits cold, humid rooms and heritage interiors where damp is a genuine concern.
Acoustics. Sound cannot travel through a vacuum, so a VIG beats a single pane of the same thickness for noise and holds its own against much bulkier units. Pilkington Spacia is rated around Rw 35 dB; tempered LandVac reaches roughly 36–39 dB depending on build-up; laminated variants do better still. A typical argon double-glazed unit sits nearer 29–32 dB. So on noise, vacuum glazing generally has the edge over standard double glazing — though a heavy laminated acoustic double-glazed unit, or an asymmetric triple, can be specified to compete where noise is the priority.
Appearance: pillars and the port
Vacuum glazing carries two visual signatures double glazing does not. The first is the support-pillar grid: a regular array of tiny dots, each around 0.3–0.5 mm across, spaced roughly every 20 mm (wider on tempered units — LandVac uses far fewer, about 267 per square metre, versus 2,600-odd on a classic annealed grid). At normal viewing distance they disappear; up close, in raking light, you can pick them out.
The second is the edge seal and evacuation (pump-out) port. Spacia and LandVac finish with a small round “button” or plug in a corner where the cavity was pumped down and sealed. AGC Fineo hides its port entirely — there is no visible plug — at the cost of a faint double reflection and a small mark. Conventional double glazing has none of this; its tell is simply the wider sightline and the spacer bar around the perimeter. Whether the pillars and port bother you is subjective, and it is worth seeing a sample in daylight before deciding. The three mainstream products differ enough here that our Spacia, Fineo and LandVac comparison is worth a read if appearance matters to you.
Lifespan, seals and the warranty gap
A sealed double-glazed unit fails in a familiar way: over 15–25 years the perimeter sealant degrades, the desiccant saturates, argon slowly escapes, and eventually moisture gets in and the unit mists internally. It is a well-understood, well-priced replacement.
Vacuum glazing’s durability rests on two things instead: the pillar array holding against roughly 10 tonnes per square metre of atmospheric pressure, and a hermetic edge seal holding the vacuum for decades. The seal is where the products diverge. Spacia uses a rigid glass-frit seal, fired hot enough to de-temper the glass — strong and fully inorganic, but brittle and more sensitive to thermal-stress cracking when the temperature difference across the panes is large. Tempered units (LandVac, Panasonic) use proprietary low-temperature seals that keep the glass toughened and flex a little to absorb that stress; Fineo uses its own undisclosed low-temperature seal with no visible port. In the United States, V-Glass is developing a metal-welded seal, but it is still pre-commercial.
Manufacturers claim vacuum retention of 25 to 60-plus years. Those are manufacturer figures, not independently verified at scale — the technology has not been in the field long enough for real-world longevity to be proven, and industry bodies are candid about that. Note too the gap between warranty and claimed lifespan: warranties run around 10 years (Spacia), 15 (LandVac) and 20 (Fineo), well short of the headline 60-year claims. That gap is a fair thing to weigh. On the other hand, a fully inorganic vacuum seal has no organic sealant or desiccant to break down, which is precisely why proponents argue it could ultimately outlast a conventional IGU. The honest position today is: promising, not yet proven.
One standards footnote worth knowing: the familiar sealed-unit standard EN 1279 explicitly excludes vacuum glass, so a VIG cannot be “EN 1279 certified.” Vacuum glazing is covered instead by ISO 19916 (Part 1 published 2018, Part 3 in 2021). If a supplier cites the wrong standard, it is a small sign they may be newer to the product.
Cost: the premium, and what narrows it
Vacuum glazing costs more than standard double glazing — as a rule of thumb, roughly two to four times the price of a like-for-like double-glazed unit. These are indicative market estimates, not quotes, and the real figure depends on size, product, installer and lead time. (Fineo tends to lead on availability at around 4–8 weeks; LandVac and Spacia can run to 10–16 weeks.) Our UK cost guide goes into the numbers in detail.
But the raw multiple flatters double glazing, because it ignores what you are really choosing between. Two things narrow the gap:
- Versus triple glazing, the premium shrinks. Triple glazing is itself well above standard double glazing in price, so a tempered vacuum unit that matches or beats it on U-value no longer looks so expensive — and it does so at a fraction of the thickness and weight.
- Versus frame replacement, the sum can flip entirely. If keeping a slim vacuum unit means retaining and restoring an existing timber frame — rather than ripping it out for a deeper double-glazed one — the glazing premium may be offset, or beaten, by not paying for new frames, joinery and making-good. On a listed building, replacement may not even be permitted.
That last point is why “which is cheaper” has no single answer. It depends entirely on the window in front of you.
Which should you choose, and when
There is no universal winner. Match the glazing to the situation.
Heritage retrofit and conservation
This is vacuum glazing’s home ground, and usually a clear win. Where you want to keep an original single-glazed sash or casement — for looks, for planning reasons, or because it is a listed building — a 6–8 mm vacuum unit fits the existing rebate and preserves the slim sightlines that standard double glazing would destroy. Slim vacuum glazing can be acceptable under Historic England guidance, assessed case by case at the conservation officer’s discretion; it is not blanket-”approved,” and you should confirm locally before committing. See vacuum glazing for listed buildings for how those conversations tend to go. Here, double glazing is often simply the wrong tool.
Standard replacement in a modern home
If you have ordinary uPVC or timber frames deep enough to take a conventional unit, and no heritage constraint, modern double glazing is usually the sensible default. It is cheaper, universally available, quick to source, and its ~1.1–1.6 U-value already meets regulations comfortably. Classic vacuum glazing would cost several times as much to land at a similar U-value — the money only makes sense if you specifically need the slimness or the extra condensation and acoustic resistance.
New build and low-energy targets
For new-build and Passivhaus-style projects the question is really vacuum versus triple glazing. Both can hit demanding U-values. Choose tempered vacuum glazing where thin, light units matter — slender sightlines, large spans where weight counts, or roof windows (VELUX’s Heritage roof window, arriving in the UK and Ireland in 2026, uses VIG to reach a whole-window Uw of 1.0, or 0.83 in its hybrid form). Choose triple glazing where upfront cost dominates and depth and weight are not a problem, since it is the cheaper route to a very low U-value. Whether the vacuum premium is justified for you is exactly the judgement our is it worth it? guide is built to help with.
The bottom line
Vacuum and double glazing are not really rivals so much as answers to different questions. On a straight U-value comparison, classic frit-sealed vacuum glass draws level with good modern double glazing — no more — while tempered vacuum glass genuinely overtakes it and rivals triple glazing. What vacuum glazing adds, in every version, is extraordinary slimness, lower weight, strong condensation resistance and a useful edge on noise. What it asks in return is a price premium of roughly two to four times, a faint pillar grid, and a durability record that still rests on manufacturer claims rather than decades of proof.
For a modern home with deep frames and no heritage constraint, standard double glazing remains the value choice. For a period or listed building where the original frames must stay, vacuum glazing is often the only way to reach modern performance without changing the window’s character. And for a new low-energy build, it becomes a considered trade of cost against thickness and weight versus triple glazing. Decide which of those you are, and the right glass is usually obvious.