What Is Vacuum Glass?
How vacuum insulating glass (VIG) works, how it compares with double and triple glazing, and where it delivers the biggest gains.
Vacuum insulating glass (VIG) is a glazing unit in which two panes of glass are separated by an evacuated gap instead of air or argon. Because the gap is a near-vacuum — a tiny fraction of atmospheric pressure — there is almost no gas left to conduct or convect heat from one pane to the other.
The result is insulation performance that traditionally required a much thicker unit. A typical VIG unit reaches a center-of-glass U-value in the range of 0.06–0.13 Btu/h·ft²·°F, with unit thickness starting at 6.3 mm — two 3 mm lites with a 0.3 mm vacuum gap between them — close to the insulating power of a triple-pane unit in the footprint of a single pane.
A gap with almost nothing in it
Heat moves through a conventional double-pane window by conduction and convection through the gas fill, by radiation between the panes, and by conduction through the edge. A vacuum gap removes the first path almost entirely: with no gas molecules to carry energy across, conduction and convection between the panes effectively disappear. What remains is radiation and edge conduction — and both can be engineered down.
Pillars: the invisible skeleton
Atmospheric pressure pushes the two panes toward each other with roughly a ton of force per square meter, so VIG units are held apart by a grid of microscopic support pillars — typically a fraction of a millimeter tall, spaced tens of millimeters apart. They are small enough to be nearly invisible in everyday view and daylight transmission, yet strong enough to keep the gap stable for decades.
The edge seal
Maintaining a vacuum for the life of the unit depends on the edge seal. THERMGLASS units use a hermetic glass-frit edge seal — a portless process, with no pump-out ports or metal bands left in the finished unit — rather than the organic sealants used in conventional insulating glass, which is why a well-made VIG unit does not rely on desiccant or gas fill replacement over time the way a standard IGU can. The frit seal sits flush with the glass faces, so a THERMGLASS unit's overall depth equals its glass stack: 6.3 mm with 3 mm lites, 8.3 mm with 4 mm lites, or 10.3 mm with 5 mm lites. Where a standard IGU frame depth or maximum performance is required, a hybrid build bonds a VIG unit to a conventional IGU cavity (argon or air fill), at roughly 20.3–26 mm overall. Some welded-edge VIG designs from other makers do add height at the perimeter — when comparing products, always confirm the edge build-up, not just the center-of-glass profile.
Where the remaining heat flow goes
With conduction and convection suppressed, radiation becomes the dominant remaining transfer path between the panes. Low-emissivity (low-E) coatings on the pane surfaces cut radiative transfer dramatically — one coated surface is standard, and two coated surfaces push performance further. Combined with a thermally broken frame, this is how a whole-window U-value around 0.13 Btu/h·ft²·°F (0.73 W/m²·K) is achieved from a unit barely thicker than single glass.
VIG vs. conventional glazing
Typical ranges for orientation-free comparison; exact values depend on makeup, coatings, and frame. Use the configurators on this site for project-specific numbers.
| Glazing type | U-value | Thickness | Notes |
|---|---|---|---|
| Single pane | ~1.04 Btu/h·ft²·°F | ~6 mm | No meaningful insulation value; heavy condensation risk. |
| Standard double pane (low-E + argon) | ~0.30 Btu/h·ft²·°F | ~24 mm | The industry baseline for residential and commercial glazing. |
| Triple pane | ~0.17–0.25 Btu/h·ft²·°F | ~36–44 mm | Best conventional performance, but heavy, thick, and demanding on frames. |
| Vacuum insulating glass | ~0.06–0.13 Btu/h·ft²·°F | 6.3–10.3 mm (3/4/5 mm lites) | Triple-pane-class insulation at single-pane thickness and a fraction of the weight. |
Where vacuum glass makes the biggest difference
- Retrofit and historic buildings, where original sash or frame depths cannot accept a 24–44 mm unit but can accept a 6.3–10.3 mm vacuum unit.
- Cold-chain and marine applications, where a warm inner pane surface keeps relative humidity high without condensation forming.
- Weight-limited installations — marine joinery, vehicles, skylights — where every millimeter and every kilogram of glass matters.
- Designs that want slim sightlines and narrow frames without giving up thermal performance.
What to compare when evaluating VIG
- Whole-window U-value (Uw), not just center-of-glass (Ucog) — frame fraction matters, typically around 20% of the opening.
- Solar heat gain coefficient (SHGC), which controls how much summer heat the glass admits alongside winter insulation.
- Certified test values — ask for NFRC 100 (US) or EN 673 (EU) data rather than marketing ranges.
- Acoustic performance, which in VIG is driven by the vacuum gap and pane thickness combination rather than gas fill.
Vacuum glass is not a new coating or a better gas fill — it is a structural rethinking of the insulating unit itself. That is why its gains do not fade as gas migrates or seals age, and why it keeps performing in the thin profiles where conventional glazing physically cannot.
THERMGLASS publishes interactive configurators so you can model U-values, condensation risk, and payback for your own project before you commit to a specification.
Model your own project
Pick a market, choose a glass makeup, and see the physics — U-value, condensation risk, and estimated payback — calculated live.
Open the configurator