What Is Vacuum Insulated Glass — And Why Does It Perform Better Than Triple Pane?

Most glazing insulates by trapping gas between two panes of glass. That gas — typically argon — reduces heat transfer compared to a single pane. Vacuum insulated glass does something fundamentally different: it removes the gas entirely, replacing the gas cavity with a vacuum so near-perfect that the primary mechanism of heat loss through the glass unit almost disappears.

Why gas is the problem in conventional IGU

Heat travels through a glazing system in three ways: conduction (through solid materials), convection (through moving fluids or gases), and radiation (through electromagnetic waves). In a conventional double-pane IGU, the gas-filled cavity is meant to address the first two — but only partially succeeds.

Argon is a poor conductor compared to air, which is why argon-filled IGUs outperform air-filled ones. But argon still conducts heat. It still convects. As the warm inner pane heats the gas near it, that gas rises, flows across to the cold outer pane, cools, sinks, and cycles back — creating a convective loop that transfers thermal energy continuously. This convective mechanism accounts for a significant share of the total heat loss in a conventional IGU.

Low-emissivity coatings address the radiation component by reflecting long-wave infrared radiation back into the space. But no coating stops convection. And no coating stops the conduction through the gas itself. The physics of a gas-filled cavity places a hard floor on how good a conventional IGU can get.

The vacuum solution: removing the medium entirely

A vacuum contains no gas molecules. No molecules means no conduction through the medium, and no convection — there is nothing to convect. The only heat transfer paths remaining are radiation (addressed by Low-E coating) and the tiny thermal bridges created by the ceramic spacer pillars and the metal edge seal.

This is why VIG can achieve U=0.40 W/m²K in a panel just 8.2mm thick. With the two dominant heat transfer mechanisms eliminated, the residual losses through radiation, spacer conduction, and edge seal are what determine the final U-value. And those losses are very small.

Anatomy of a VIG panel

Understanding what makes VIG work — and what makes it difficult to manufacture — comes down to its five functional components.

The glass substrates

Both panes must be fully tempered. This is non-negotiable: the vacuum creates atmospheric pressure of approximately 100,000 Pa acting to compress the panel. On a 1m × 1m panel, that's roughly 10 tonnes of compressive force. Only fully tempered glass has the strength to withstand this load without failure. Critically, glass cannot be tempered after VIG assembly — so the tempering must be performed first, to very precise flatness tolerances.

The ceramic micro-dot spacers

To keep the two panes 0.2mm apart under the compressive atmospheric load, an array of ceramic spacers is embedded in the vacuum gap. These are typically 0.5–0.8mm in diameter, arranged in a regular grid with spacings of 25–40mm depending on glass thickness. The spacers are the only solid thermal bridge crossing the vacuum gap — their small contact area and low thermal conductivity are carefully optimised to minimise this bridging loss.

The metal edge seal

The perimeter of the panel is sealed with a low-temperature metal solder — not epoxy, not silicone. Epoxy and polymer sealants off-gas over time, contaminating the vacuum and causing progressive performance degradation. Metal solder is hermetic and chemically stable across the operating temperature range. The sealing process is performed under vacuum, with the solder melted and flowed into position to form an airtight perimeter bond.

The Low-E coating

A Low-E coating on the inner surface of the outer pane (facing the vacuum) addresses the radiation component of heat transfer. Double silver Low-E coatings — such as the D80 used in VIG Horizon's 4TL+V+4T configuration — achieve emissivities below 0.03, reflecting over 97% of long-wave infrared radiation back across the vacuum gap. This is what makes U=0.40 achievable rather than U=0.55.

The getter

Even after perfect vacuum sealing, trace gas molecules are always present, and additional molecules slowly permeate through the glass and seal over decades. A small getter device — typically a needle-shaped housing containing reactive materials — is placed within the vacuum space. As residual gas molecules contact the getter, they are chemically bound and removed from the gas phase, maintaining the vacuum quality over the unit's rated life. The getter is what allows VIG to maintain its performance for 15 years or more without recharging.

Performance: the numbers that matter for Canada

★ Centre-of-glass U-value. TÜV Rheinland Report CN25TTIK-002, EN 673:2011, September 2025.

Why this matters for Canadian fabricators

Canada's building codes are moving toward performance thresholds that gas-filled triple IGU approaches but struggles to clear consistently — and does so at the cost of 36–44mm of frame depth and 28 kg/m² of structural load. For heritage projects, that thickness is often physically incompatible with existing frame pockets. For net-zero builders, the weight adds structural cost throughout the building system.

VIG doesn't just perform better than triple IGU on U-value. It performs better at a third of the thickness and at significantly lower weight. That combination — performance, thinness, and lightness simultaneously — is not achievable with any gas-filled technology. It requires the vacuum.