Vacuum Insulated Glass vs Double Glazing

Quick answer

Vacuum Insulated Glass (VIG) and conventional double glazing are both ways to reduce heat transfer through a window, but they solve the problem through different physics. VIG uses a very narrow evacuated cavity held apart by an array of spacer pillars, eliminating gas-related heat transfer while relying on a low-emissivity coating and careful pillar and edge-seal design for the remaining heat paths. Conventional double glazing uses a wider cavity filled with air or argon, separated by a perimeter spacer, and relies on the low-e coating and the insulating gas for its thermal performance.

VIG's main advantages are typically a slimmer profile and a different thermal-performance headroom in the available depth. Conventional double glazing's advantages are typically a mature supply chain, lower unit cost in most markets, broader size availability, and simpler specification through established window systems. The right choice depends on the project: rebate depth, frame compatibility, weight, heritage or planning constraints, and budget all matter.

This page does not claim that VIG is universally better than double glazing. For many projects — particularly new-build with a standard rebate depth — conventional double glazing remains the simpler and more economical specification. For projects where the rebate cannot accept a thick IGU, where the original frame must be retained, or where slim sightlines are a design priority, VIG may be the more competitive choice.

At-a-glance comparison

The table below sets out the comparison at a glance. Several rows are deliberately written qualitatively rather than as a single number, because a single universal figure would mislead.

How the two systems differ

Vacuum Insulated Glass (VIG)

Primary sourcePer EAD 300021-00-0404 (EOTA, February 2019), a VIG unit is "a glazing product consisting of two panes of glass, separated by an array of spacer pillars and sealed along the periphery, whereby the space between the glass panes is evacuated to a pressure below 1 Pa (10⁻² mbar)." The hermetic edge seal is made on the basis of solder glass. The low-emissivity coating on a cavity-facing surface suppresses radiative radiation across the gap.

The evacuated cavity is the defining feature. Without gas, the dominant heat-transfer mechanisms in a conventional IGU — gas conduction and convection — are removed. The remaining paths are radiative transfer (addressed by the low-e coating), solid conduction through the spacer pillars, and solid conduction through the edge seal. See the VIG pillar guide for the full construction overview.

Conventional double glazing

Primary sourcePer EN 1279-1:2018 (the European standard for insulating glass units, which explicitly excludes vacuum insulating glass from its scope and refers readers to ISO 19916), a conventional insulating glass unit (IGU) consists of two or more glass panes separated by one or more sealed cavities. The cavity is filled with air, argon, or another gas; a perimeter spacer maintains the cavity width; a desiccant inside the spacer absorbs residual moisture; and a primary and secondary edge seal keep the cavity sealed over the service life.

In a typical modern double-pane IGU, the cavity is filled with argon (a poor heat conductor) and at least one of the cavity-facing surfaces carries a low-emissivity coating. The combination of insulating gas and low-e coating is what delivers the thermal performance.

Thickness and why it matters

The most visible structural difference between VIG and double glazing is overall thickness. The reason is the cavity: VIG's evacuated cavity is roughly 0.1 mm wide; a conventional double-pane IGU cavity is typically 12 to 20 mm. Total unit thickness follows from there.

Example product constructions

Manufacturer-reportedExamples of manufacturer-reported total unit thicknesses (illustrative, not exhaustive):

• Pilkington Spacia — described in Pilkington technical literature as having a total unit thickness of just over 6 mm.
• Fineo — manufacturer-reported total thickness in the region of 7 to 8 mm (product-variant dependent).
• LandVac — manufacturer-reported total thickness of approximately 8.3 mm (with 4 mm lites).
• VacuMax (Vitro Architectural Glass) — manufacturer-reported 8.3 mm minimum with 4 mm lites, 12.3 mm maximum with 6 mm lites.
• Standard double-pane IGU — typically a 4 mm / 16 mm / 4 mm construction (24 mm total) or 4 mm / 20 mm / 4 mm (28 mm total) for argon-filled low-e units.

These figures are manufacturer-reported and product-specific. Always confirm against the current datasheet for the product being specified.

Why thickness matters

Thickness matters because the window rebate, glazing bead, and any existing frame dictate what will physically fit. Several common project situations make thickness a binding constraint:

• Existing timber frames in older buildings, where the glazing rebate was sized for single glazing or early double glazing and cannot accommodate a modern 24 to 28 mm unit without altering the frame.
• Vertical-sliding sash windows, where slim sightlines and reduced sash weight are part of the design.
• Heritage windows in listed or conservation-sensitive buildings, where planning rules typically require retention of the original frame and sightlines.
• Steel and metal heritage windows (e.g., Crittall-style frames), which have particularly narrow profiles.
• Retrofit projects generally, where the brief is to improve thermal performance without disturbing the existing building fabric.

See the heritage windows application entry for a deeper discussion.

Thermal performance: Ug vs Uw

Ug is the centre-of-glass U-value — a property of the glazing alone, measured at the centre of the pane under a defined temperature differential, calculated per EN 673 or ISO 10292. Uw is the whole-window U-value, additionally accounting for the frame, the edge-of-glass zone, and the spacer system. EAD 300021-00-0404 requires the ETA to state the U-value truncated to three decimals.

Comparing a VIG Ug to a double-glazed Uw — a common error in product literature and consumer comparisons — overstates VIG's whole-window performance.

Manufacturer-reported ranges (centre-of-glass Ug)

Manufacturer-reported

• VIG with a single low-e coating — manufacturer-reported Ug typically in the region of 0.4 to 0.7 W/m²K. Specific products may report figures within or outside this range.
• Argon-filled low-e double-pane IGU — product literature from Pilkington (Optitherm S1 Plus) and Saint-Gobain Glass (PLANITHERM / COOL-LITE examples) reports centre-of-glass Ug around 1.0 W/m²K for specified low-e, argon-filled double-glazing build-ups. Other constructions report higher values; the exact figure is product-specific.
• Triple-pane argon-filled low-e IGU — typically lower Ug than double-pane, at the cost of a thicker and heavier unit.

These are ranges, not universal values. The exact figure for any specific construction must be read from the relevant test report.

Weight

A VIG unit is generally thinner and lighter than a triple-pane IGU of comparable thermal performance. The comparison against double glazing is less clear-cut:

• A standard 4 mm / 16 mm / 4 mm double-pane IGU contains 8 mm of glass. At the conventional soda-lime glass mass factor of 2.5 kg/m² per millimetre of thickness, the two plies weigh 8 mm × 2.5 kg/m²/mm = 20 kg/m², before spacer and sealant mass. A VIG unit of similar glass-ply configuration typically weighs less, but the exact figure depends on the specific VIG product and any laminated plies.
• Where the VIG product uses thicker glass plies (e.g., 6 mm) or laminated plies for safety, the weight advantage narrows or disappears.
• For sash windows in particular, lower weight can reduce the load on counterweights, balances, and hinges. The total sash weight matters, not just the glazing weight.

Treat any specific weight claim as product-specific and verify against the relevant manufacturer datasheet. This page does not quote a universal weight-saving figure.

Heritage and retrofit suitability

The slim profile of VIG makes it a strong candidate in heritage retrofit situations where the existing frame cannot accept a thicker IGU. The principle is straightforward: where the rebate cannot accommodate a 24 to 28 mm double-pane IGU, a VIG unit in the 6 to 10 mm range may still fit.

Heritage retrofit situations where VIG may be worth specifying include:

• Traditional sash windows with shallow glazing rebates.
• Heritage timber frames where planning or conservation rules require retention of the original frame.
• Historic steel windows (Crittall-style and similar) with particularly slim profiles.
• Listed-building or conservation-area projects where any change to the visible frame is constrained.

VIG does not automatically confer listed-building consent. Heritage approval is project-specific and depends on the local planning regime, the building's listing status, and the judgment of the responsible conservation officer. See the VIG pillar heritage section for the full framing.

Even in a heritage project, conventional double glazing may be the right answer where the existing rebate is sized for a double-pane unit and the heritage priority is unobtrusive replacement rather than maximum thermal performance.

New-build suitability

For new-build or full-window-replacement projects, conventional double glazing is often the simpler and more economical specification. The reasons are structural to the supply chain rather than to the technology:

• Mature window systems. Frame systems designed for double glazing are widely available, well documented, and supported by tooling across the window-fabrication industry.
• Established supply chains. Standard double-pane IGUs are made locally in many markets; lead times are short; replacement units are easy to source.
• Broader manufacturer choice. Hundreds of IGU manufacturers serve most regions; brand and price competition keep cost down.
• Easier specification. Window energy ratings (WERs) and product declarations are widely available for double glazing; the procurement process is well understood.
• Lower unit cost in most markets. Double glazing is the commodity product; VIG is the specialist product.

VIG is not an automatic pick for new-build. There are new-build cases where VIG makes sense — for example, designs that specify unusually shallow glazing rebates, slim sightlines as a defining architectural feature, or particularly demanding thermal targets — but they are exceptions rather than the rule.

Acoustic performance

Acoustic insulation depends on glass thickness, interlayer presence, asymmetry between panes, frame design, edge seals, and installation — not on whether the cavity is evacuated or gas-filled. This is a common misconception about VIG.

Practical implications:

• A VIG unit with two 4 mm annealed plies delivers different acoustic performance from a VIG unit with a laminated inner ply. The evacuated cavity itself is not the acoustic differentiator.
• A double-pane IGU with asymmetric glass thickness (e.g., 4 mm / 6 mm) and a laminated outer ply can deliver high acoustic ratings. Double glazing with acoustic lamination is widely available.
• Acoustic figures should always be quoted for the specific tested construction: glass thickness, interlayer presence, frame, and edge-seal design. A single number for "VIG acoustic performance" or "double-glazing acoustic performance" is not meaningful.

Safety glazing

Both VIG and double glazing can be produced with safety-glass constructions, but the option set is different:

• Annealed — the baseline; not a safety-glass classification under most codes.
• Toughened (tempered) or heat-strengthened — required by safety-glazing codes in many positions (overhead, sloped, door-side, low-level). EAD 300021-00-0404 references EN 12150-2 (thermally toughened soda-lime silicate safety glass) and EN 1863-2 (heat-strengthened soda-lime silicate safety glass). Whether a particular VIG product can be supplied toughened depends on the manufacturer.
• Laminated — provides post-breakage retention. EAD 300021-00-0404 explicitly defines laminated VIG (LVIG) as a separate construction in which one or both plies are laminated glass per EN 14449.

Double glazing has the broader and more standardised safety-glass option set. VIG safety-glazing options exist but are product-specific and manufacturer-specific; not every manufacturer offers every option. Confirm with the manufacturer that the proposed variant carries the relevant third-party certification for the project jurisdiction.

See the pillar page's annealed, toughened and laminated section for the full framing.

Durability

There is no single industry-wide service-life figure for either system. Both depend on product-specific design, manufacture, installation, and maintenance.

Conventional double glazing — common considerations

• Edge-seal failure. The primary edge seal in an IGU is typically a polyisobutylene (PIB) primary seal and a polysulfide or silicone secondary seal. Edge-seal failure leads to moisture ingress, internal condensation, and loss of gas fill where present.
• Gas retention. Argon-filled units lose some gas over time; the rate depends on the edge-seal design and the manufacturing quality.
• Desiccant capacity. The desiccant in the perimeter spacer absorbs residual moisture during manufacture and any small moisture ingress over service life. Once saturated, internal condensation can occur.

VIG — common considerations

• Vacuum retention. The dominant failure mode described in the technical literature is breach of the hermetic edge seal, after which the cavity vents and the unit must be replaced.
• Getter effectiveness. The getter sorbs residual gas and any slow leakage over time; its capacity is part of the product design.
• Thermal cycling. ISO 19916-3:2021 specifies test methods for evaluating VIG performance under temperature differences, which is one form of evidence used in qualification.
• Mechanical impact. Peer-reviewed research (Schulz et al., 2022) found that VIG units failed at pendulum-impact drop heights below those prescribed by EN 12600 for monolithic glass, with pillar-to-glass contact identified as a fracture origin. ISO 19916-4:2026 now provides a VIG-specific pendulum-impact classification.

Condensation

Improved glazing performance changes the surface temperature of the glass, which changes the condensation behaviour on the inside and outside of the window.

• Interior condensation. A low centre-of-glass U-value keeps the inner glass surface temperature closer to room temperature, reducing the risk of condensation on the room-side surface. Edge-of-glass performance is still relevant.
• Exterior condensation. In high-performance glazing, the outer surface can drop below the external dew point under clear-sky radiative cooling, and condensation forms on the outside. This is a sign of good thermal performance, not a failure.
• Between-pane condensation (only relevant to IGUs with a sealed gas-filled cavity). Visible moisture or fog between the panes of a double-pane IGU indicates edge-seal failure and the need for unit replacement. VIG has no internal cavity in the same sense; if the cavity loses vacuum, the symptom is reduced thermal performance rather than visible internal fog.

Cost

As a specialist product with a smaller manufacturer base, VIG is generally more expensive per square metre than commodity double glazing. The exact premium varies by manufacturer, region, configuration, and order size, and there is no current cross-market figure that VIG Guide would defend.

Total project cost is not the same as glazing unit cost. Several project-specific factors change the economics:

• Frame retention. Where VIG allows the existing frame to be retained rather than fully replaced, the saving on frame, demolition, and finishing work can offset a higher glazing unit cost.
• Frame rework. Where a thick IGU does not fit the existing rebate, the frame must be modified or replaced. VIG may avoid this.
• Installation. Specialist products may require specialist installers; double glazing is widely installed.
• Logistics. VIG is a smaller-volume product; transport, handling, and replacement-unit sourcing can be more involved.
• Project scale. A heritage retrofit on a single window frames the cost differently from a multi-unit new-build procurement.

Availability and lead time

• Double glazing — mature global supply chain; local fabrication is common in most markets; standard sizes are typically stocked; replacement units are easy to source.
• VIG — specialist product with a smaller manufacturer base; distribution is regional; lead times are product-specific; cross-border sourcing may be required in some markets.

This page does not quote a universal VIG lead time. For any specific project, confirm current availability and lead time with the manufacturer or authorised distributor.

Repair and replacement

Both VIG and double glazing are sealed units that must be replaced as a whole when they fail. The differences are in the replacement process:

• Matching older installations. Where the original product is no longer manufactured, sourcing a like-for-like replacement may be difficult for VIG; for standard double glazing, equivalent sizes and constructions are widely available.
• Supplier continuity. For VIG, long-term supplier support and replacement availability are worth considering at the specification stage. The specialist-manufacturer base means fewer fallback options.
• Warranty support. Both products carry manufacturer warranties. The terms and the in-field support infrastructure differ by manufacturer.

Sustainability

A sustainability comparison of VIG and double glazing is not a one-line answer. It depends on what is being measured over what period.

• Operational energy. Both systems reduce heat transfer through the window compared with single glazing. Higher-performing systems reduce operational energy use over the service life.
• Embodied carbon. Embodied carbon depends on the glass quantity, the spacer and edge-seal materials, and the manufacturing process. This page does not quote a universal embodied-carbon comparison; consult product-specific EPDs (Environmental Product Declarations) where available.
• Frame retention. In heritage retrofit, retaining the existing frame avoids the embodied carbon of manufacturing and installing a replacement frame. This can be a meaningful sustainability advantage of a slim-profile glazing choice, irrespective of the cavity construction.
• Service life. A longer-lasting unit postpones replacement and the associated embodied carbon, but only if the longer life is real and not a design assumption.

This page does not claim that VIG is greener than double glazing or vice versa. A full life-cycle assessment is project-specific.

When VIG may be the better fit

VIG may be the more competitive choice where one or more of the following conditions apply:

• The existing rebate is too shallow for a standard double-pane IGU.
• The existing frame must be retained — for heritage, conservation, planning, or cost reasons.
• Slim sightlines are a design priority — for heritage, sash, steel, or contemporary narrow-profile designs.
• The thermal target is high and the available glazing depth is constrained.
• Weight matters — for example, sash windows with weight-sensitive balances.

This list is not a recommendation that VIG is better. It is a list of project conditions under which VIG may be the more competitive choice. The actual decision depends on the specific product, frame, project economics, and planning regime.

When conventional double glazing may be the better fit

Conventional double glazing may be the more competitive choice where one or more of the following apply:

• Standard new-build with a typical rebate depth designed for double glazing.
• Budget-sensitive projects where commodity pricing matters.
• Standard replacement of existing double glazing, with the same construction.
• Large-volume procurement with multiple window types and sizes.
• Easy replacement is a priority, for example rental housing stock or commercial property.
• No thickness constraint — the rebate is deep enough for any IGU.
• Mature frame systems are required, with broad market availability.

For most of these situations, conventional double glazing is the simpler, more economical, and more flexible specification. VIG is the specialist alternative.

Decision framework

Consider VIG if…

• The existing rebate is too shallow for the double-pane IGU you would otherwise specify.
• The original frame must be retained for heritage, planning, or cost reasons.
• Slim sightlines are a defining design feature.
• Sash weight is a constraint.
• A higher thermal performance is needed than a standard double-pane IGU can deliver in the available depth.
• Specific manufacturer and product data — including an ETA where relevant, declared Ug and Uw, safety classification, and acoustic test data — are available and have been reviewed.

Consider conventional double glazing if…

• The rebate is sized for a standard double-pane IGU.
• The project budget is the binding constraint.
• Standard availability, local fabrication, and easy replacement matter more than maximum thermal performance.
• No thickness or weight constraint applies.
• Mature frame systems are required.

Ask your supplier

1. What Ug is tested for this exact construction, and what is the test standard?
2. What Uw is declared for the actual frame and spacer combination being specified?
3. What is the exact glass construction (each ply thickness, interlayer, coating position)?
4. What safety classification does the unit carry for the project jurisdiction?
5. Which test standards is the unit certified against (ISO 19916, EN 1279, ASTM E2190, others)?
6. What are the warranty terms, and what do they cover?
7. What are the maximum dimensions available for this product?
8. What is the current lead time and the replacement-unit availability?
9. What is the frame compatibility — what rebate depth and bead geometry does the product assume?
10. For heritage projects: does the proposal require planning or listed-building consent, and has that consent been confirmed?

FAQ

Common questions buyers and specifiers ask when comparing VIG and conventional double glazing.

Sources

Sources supporting this page follow the VIG Guide tier system used on the pillar page. Where a specific value is sourced to manufacturer literature, the body text labels it as manufacturer-reported.

Primary — standards and assessment documents

• EAD 300021-00-0404 — Vacuum insulating glass units. EOTA, February 2019. Defines VIG and LVIG; references ISO 19916-1 and EN 1279 (with adaptations); specifies assessment methods including pendulum-impact, temperature differentials, and U-value declaration.
• EN 1279-1:2018 — Glass in building — Insulating glass units — Part 1: Generalities, system description, rules for substitution, tolerances and visual quality. CEN. Its scope explicitly excludes vacuum insulating glass.
• EN 673:2011 — Glass in building — Determination of thermal transmittance (U value) — Calculation method. CEN.
• EN 572-1:2012+A1:2016 — Glass in building — Basic soda-lime silicate glass products — Part 1: Definitions and general physical and mechanical properties. CEN. Basis for the conventional 2,500 kg/m³ soda-lime glass density used in the weight example.
• ISO 10292:1994 — Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing. ISO.
• ISO 19916-1:2018 — Glass in building — Vacuum insulating glass — Part 1 (under revision; ISO/DIS 19916-1 in development). ISO.
• ISO 19916-3:2021 — Glass in building — Vacuum insulating glass — Part 3: Test methods for evaluation of performance under temperature differences. ISO.
• ISO 19916-4:2026 — Glass in building — Vacuum insulating glass — Part 4: Pendulum impact testing and classification. ISO.

Primary — peer-reviewed research

• Schulz, I., Kocer, C., Paschke, F., Schneider, J. (2022). The Performance of Vacuum Insulating Glazing Units Subjected to a Soft Body Impact. Challenging Glass Conference Proceedings Vol. 8. DOI 10.47982/cgc.8.443. Reports pendulum-impact testing of VIG units against EN 12600, finding failure at drop heights below the standard's prescriptive level.

Manufacturer-reported — product examples

Examples cited on this page are illustrative, not endorsements. VIG Guide does not rank or recommend specific products.

• Double glazing examples — Pilkington Optitherm S1 Plus product literature reports Ug 1.0 W/m²K when incorporated in a specified double-glazing build-up. Saint-Gobain Glass product literature for PLANITHERM / COOL-LITE reports Ug 1.0 W/m²K for specified low-e, 90% argon-filled double-glazing build-ups. These are manufacturer-specific examples, not a universal double-glazing value.
• Pilkington Spacia — manufacturer technical literature describing total unit thickness of just over 6 mm.
• Fineo — manufacturer-reported total thickness in the region of 7 to 8 mm (product-variant dependent). See brand profile.
• LandVac — manufacturer-reported total thickness of approximately 8.3 mm with 4 mm lites. See brand profile.
• VacuMax (Vitro Architectural Glass) — manufacturer-reported 8.3 mm minimum with 4 mm lites, 12.3 mm maximum with 6 mm lites.

Methodology references

• VIG Guide Methodology — source classification system used on this page.
• Editorial Policy — sourcing standards and correction procedure.
• Commercial Disclosure — separation of editorial and commercial content.

What this page does not rely on

This page does not rely on reseller websites, SEO blogs, or AI-generated summaries for technical claims. Cross-market cost figures, acoustic ranges, and lifespan numbers are not stated unless they can be tied to a primary or manufacturer source.