Vacuum Insulated Glass (VIG)

1. Product Overview

Vacuum insulated glass (VIG) is a high-performance flat glass product that uses a sealed vacuum cavity as its primary insulating layer. Its operating principle is similar to that of a vacuum flask: air is evacuated from the space between two parallel glass panes to create a sealed, low-pressure cavity. This greatly reduces heat transfer through gas conduction and convection, while also improving acoustic insulation compared with conventional gas-filled insulating glass units.

The product is manufactured in accordance with GB/T 38586-2020, Vacuum Insulating Glass. Different substrates, edge-sealing systems and functional coatings can be specified to suit individual requirements. Typical applications include building envelopes, industrial equipment and transport facilities where thermal efficiency and acoustic comfort are important.

Conventional vacuum glass manufacturing often uses a two-step process. The glass panes are first edge-sealed, after which the cavity is evacuated through a dedicated port that must then be sealed separately. These separate operations involve additional handling and can place greater demands on production consistency and efficiency.

SHEN-SHILEI uses a one-step vacuum glass manufacturing process that integrates glass assembly, edge sealing, high-temperature degassing, evacuation and final sealing within a sealed vacuum chamber. By carrying out these operations within an integrated process, without intermediate exposure to ambient air, the method is designed to improve consistency in cavity vacuum conditions and the reliability of the edge-seal structure while shortening production cycles. For more details, see the one-step vacuum glass manufacturing process.

2. Structure and Components

The basic structure of vacuum insulated glass consists of five main components: glass substrates, a micro-support pillar array, a vacuum cavity, an edge-sealing system and an internal getter.

2.1 Glass Substrates

The glass substrates provide the structural foundation and optical properties of the unit. Depending on the application, they may be made from float glass, fully tempered glass, heat-strengthened glass or laminated glass. Typical substrate thicknesses range from 3 to 12 mm.

All cutting, edge grinding, drilling and heat-treatment operations must be completed before vacuum sealing. Further processing after sealing is not normally possible because it may disturb the unit’s stress balance or compromise the vacuum seal.

Low-emissivity (Low-E) glass is an important consideration in vacuum glass design. At least one pane should incorporate a Low-E coating. Because radiative heat transfer can account for a substantial proportion of heat transfer across the vacuum cavity, the presence of a Low-E coating—and differences in its surface emissivity—can significantly affect the thermal insulation performance of the finished unit. Where required, the coating can be applied to a surface facing the vacuum cavity to reduce radiative heat transfer.

2.2 Micro-Support Pillar Array

The pressure inside the vacuum cavity is much lower than the external atmospheric pressure. Each square metre of glass can therefore be subjected to an atmospheric load equivalent to approximately 10 tonnes of force. A regularly arranged array of micro-support pillars is placed between the two panes to maintain the cavity gap and distribute the load.

The pillars are commonly made from stainless steel or titanium alloys. Typical diameters are 0.3–0.5 mm, while their height corresponds to the vacuum gap, usually around 0.1–0.3 mm. The pillars are arranged in a defined pattern, with hundreds of support points per square metre. Their very small projected area helps limit their effect on visible light transmission.

2.3 Vacuum Cavity

The vacuum cavity is the sealed space formed by the two glass panes and the perimeter edge seal. Its initial internal pressure is specified at ≤0.1 Pa, corresponding to a high-vacuum condition.

The cavity contains no insulating gas fill; instead, it contains the support pillars and getter. It is the core of the unit’s thermal and acoustic performance. Because the vacuum gap is much thinner than the gas space in conventional insulating glass, a VIG unit can achieve high thermal performance with a relatively slim overall profile. Depending on the configuration, its overall thickness may be approximately one-sixth that of a triple-glazed, double-cavity insulating glass unit, with a potential weight reduction of more than 10 kg/m².

2.4 Edge-Sealing System

The edge seal is essential to maintaining the vacuum over the product’s service life. Common approaches include glass-frit sealing, metal sealing and organic adhesive sealing.

Glass-frit sealing uses a low-melting-point glass material that is heated until it bonds with the substrates. It offers strong hermetic-sealing and weather-resistance characteristics and is widely used in architectural products. Metal sealing can use lower sealing temperatures and may help preserve the strength of heat-treated substrates, depending on the process. Organic adhesive sealing is comparatively simple and may offer cost advantages, but its suitability depends on the service environment and performance requirements.

2.5 Internal Getter

An alloy getter is installed inside the vacuum cavity to absorb small amounts of gas gradually released by the glass and sealing materials during service. By capturing residual and released gases, the getter helps maintain the vacuum level over time and is an important component in long-term vacuum stability.

The getter capacity is selected according to the intended service life and expected gas load. It helps compensate for outgassing and limited gas ingress, although actual long-term performance depends on the complete unit design and manufacturing quality.

3. One-Step Vacuum Glass Manufacturing Process

The vacuum insulated glass manufacturing process plays an important role in cavity vacuum consistency, edge-seal reliability and long-term product performance.

Traditional two-step manufacturing involves several separate operations, including substrate preparation, support pillar placement, glass assembly, edge sealing, evacuation and final sealing. Since edge sealing and evacuation are carried out in different stages or on different equipment, intermediate handling can expose the unit to ambient air and introduce moisture or residual gases. A separate evacuation port is also required, creating an additional sealing point and a potential design limitation.

In the one-step process, glass assembly, edge sealing, high-temperature degassing, evacuation and final sealing are integrated within the same sealed vacuum chamber. The process is carried out under controlled vacuum conditions, avoiding intermediate exposure to ambient air. Its main stages are as follows.

First, the prepared glass substrates and support pillars are loaded into the vacuum chamber under clean conditions. The chamber is evacuated to the specified pressure, and the substrates are heated to approximately 350°C to remove moisture and residual gases adsorbed on the glass surfaces and within the materials. This degassing stage is intended to reduce the amount of gas released during subsequent service.

Next, the upper and lower glass substrates are accurately aligned and assembled, and the perimeter edge seal is formed under vacuum. Maintaining the vacuum environment during sealing helps prevent unwanted gas from entering the cavity. After the edge seal is completed, final sealing is carried out inside the chamber without the need for a separate evacuation port, eliminating the associated port-sealing feature.

By reducing intermediate handling, the one-step process can lower the risk of contamination and handling damage. It is designed to improve initial vacuum consistency, reduce sealing defects and support more consistent production quality. The integrated cycle can also shorten manufacturing time from several hours to tens of minutes, depending on the product configuration and production conditions, providing a basis for higher-throughput manufacturing.

Combined with an internal getter, effective degassing and reliable sealing support the long-term vacuum stability of the finished product. Actual service performance depends on the glass configuration, materials, process parameters and quality-control procedures.

4. Core Performance Principles

4.1 Thermal Insulation

Heat is transferred through three main mechanisms: conduction, convection and radiation. Vacuum insulated glass reduces or controls these mechanisms through its structure.

Conduction: The gas molecule density inside the vacuum cavity is extremely low, substantially reducing gas-phase heat conduction. A small amount of solid-state heat transfer remains through the support pillars, but overall conductive heat loss can be much lower than in conventional gas-filled insulating glass.

Convection: The vacuum environment prevents bulk gas movement within the cavity, effectively eliminating the internal convective heat-transfer path found in conventional insulating glass units.

Radiation: Unlike conduction and convection, thermal radiation can travel across a vacuum. Low-E coatings are therefore important for controlling radiative heat transfer. By reflecting a large proportion of long-wave infrared radiation, a suitable Low-E coating can further reduce the overall heat-transfer coefficient. Depending on the glass configuration and test conditions, high-performance products may achieve a U-value as low as 0.4 W/(m²·K).

Effect of Low-E Coatings on Vacuum Insulated Glass Thermal Performance

Surface emissivity plays an important role in controlling radiative heat transfer across the vacuum cavity. The following comparison illustrates how different Low-E configurations may affect the thermal performance of vacuum glass.

Note: Values are based on the supplied comparison data. Confirm the glass structure notation and U-value test conditions before publication.

Thermal Performance Comparison of Different Glazing Configurations

The thermal performance of glazing depends on both its structure and the emissivity of the glass surfaces. The following comparison shows the differences in overall thickness and U-value between conventional insulating glass, single vacuum glazing, hybrid vacuum insulating glass, and double vacuum glazing.

Note: Values are reproduced from the supplied comparison table. Confirm the glass structure notation, surface emissivity definitions, and U-value test conditions before publication.

4.2 Acoustic Insulation

Sound transmission requires a medium, so the vacuum cavity interrupts the airborne sound path between the two panes. Vacuum insulated glass can therefore provide better acoustic insulation than conventional gas-filled insulating glass of comparable thickness, particularly for certain low- and mid-frequency noise conditions.

Sound can still travel through solid components, including the glass substrates, support pillars and edge-sealing system. Optimising pillar layout and the damping characteristics of sealing materials can help improve acoustic performance across the frequency range. Typical products may achieve a weighted sound reduction index (Rw) of ≥36 dB, while higher-performance configurations may exceed 39 dB, depending on the construction and test method.

4.3 Condensation Resistance

There is no liquid water or water vapour within a properly sealed vacuum cavity, so internal condensation does not occur under normal conditions. The strong thermal insulation performance can also help keep the room-side glass surface closer to indoor temperature, reducing the likelihood of surface condensation or frost in cold weather.

Under suitable product and installation conditions, the interior glass surface may remain free of condensation even when the outdoor temperature reaches −40°C. Actual results depend on indoor humidity, surface temperature, frame design, installation details and the product’s tested performance.

4.4 Wind-Load Resistance

The two glass substrates are connected by the edge seal and supported by the pillar array, forming an integrated structure that distributes loads. Depending on the glass construction, vacuum glass may offer higher wind-load resistance than conventional glass of comparable thickness.

For example, a 4 mm vacuum glass configuration may provide wind-load resistance exceeding that of an 8 mm monolithic glass pane. Tempered substrates can further improve mechanical strength and may be suitable for façade applications when the complete glazing system meets the project’s structural requirements.

Vacuum insulated glass is also less sensitive to changes in altitude than sealed gas-filled glazing systems because its cavity is already under vacuum. Its cavity does not undergo the same pressure-driven expansion or contraction caused by altitude differences. The overall thermal performance of an installed unit, however, still depends on its construction, orientation and boundary conditions.

5. Key Technical Specifications

The following values are representative technical indicators for selected products. The applicable product configuration and test conditions should be confirmed against the relevant product specification and GB/T 38586-2020.

• Vacuum performance: Initial cavity pressure ≤0.1 Pa. Vacuum retention after durability testing must meet the applicable standard requirements.
• Thermal performance: U-value ≤2.0 W/(m²·K) for standard configurations; as low as 0.4 W/(m²·K) for selected Low-E-enhanced configurations.
• Acoustic performance: Weighted sound reduction index (Rw) ≥36 dB for typical configurations; selected high-performance constructions may exceed 39 dB.
• Dimensional tolerance: For units with a side length below 1,000 mm, the dimensional deviation is ±2 mm. The difference between the diagonals should not exceed 0.2% of their average length.
• Weathering performance: Following applicable UV exposure, temperature cycling and constant-temperature/humidity testing, units should show no fogging or leakage and must meet the required vacuum-retention criteria.
• Mechanical performance: Wind-load resistance must meet the relevant requirements for the intended building application. For products using tempered glass substrates, the specified surface compressive stress is ≥90 MPa.

Actual values vary with glass thickness, coating type, edge-seal design, dimensions and test method. Where performance is critical, project-specific test reports should be consulted.

6. Product Classifications

Vacuum insulated glass can be classified according to cavity structure, substrate type, edge-sealing method and functional configuration.

By cavity structure: Products include single-vacuum-cavity units, composite structures combining a vacuum cavity with a gas-filled cavity, and multiple-vacuum-cavity structures. Single-cavity VIG offers a slim profile and a relatively straightforward construction. Composite units combine the thermal performance of a vacuum cavity with the characteristics of a gas-filled glazing cavity and may be considered for certain façade applications.

By substrate type: Options include float-glass VIG, tempered VIG and laminated VIG. Tempered VIG offers higher mechanical strength and is widely considered for architectural applications. Laminated VIG can provide improved impact protection and may be specified for overhead, elevated or security-related applications when the complete construction meets the relevant safety requirements.

By edge-sealing method: Products may use glass-frit, metal or organic adhesive sealing. Each approach has different processing requirements, durability characteristics, cost implications and suitable applications.

By functional configuration: Products include standard configurations and Low-E-enhanced configurations. The latter use a low-emissivity coating, typically on a surface facing the vacuum cavity, to reduce radiative heat transfer and improve thermal insulation.

Vacuum Insulated Composite Glass

In practical window and glazing applications, vacuum glass is often combined with insulating glass to form Vacuum Insulated Composite Glass. In a typical configuration, a vacuum glass unit is combined with an additional pane of flat glass to create a hybrid glazing unit with both vacuum and insulating cavities.

Common configurations include vacuum glass + insulating glass, insulating glass + vacuum glass + insulating glass, and vacuum glass + insulating glass + vacuum glass. These composite structures can also improve safety and acoustic insulation performance, depending on the glazing configuration and the specifications of the individual glass units.

7. Service Life and Reliability

The service life of vacuum insulated glass can be considered in two aspects: mechanical service life and vacuum service life.

Mechanical service life refers to the ability of the edge-sealing structure to withstand self-weight, wind loads and temperature-related stresses without cracking or failing. Structural analysis can be used to assess stresses at the edge seal under combined loading conditions. The actual safety margin depends on the materials, geometry, design assumptions, installation conditions and test results. The controlled sealing conditions of a well-managed one-step process can help improve production consistency.

Vacuum service life refers to the period during which the cavity maintains an effective vacuum level. It is mainly affected by material outgassing, gas permeation and the capacity of the getter. The glass substrates, sealing materials and support pillars are selected to limit outgassing. High-temperature degassing during the one-step manufacturing process helps remove residual gases, while the internal getter captures gases released during service.

Together, material selection, effective degassing, a reliable edge seal and sufficient getter capacity support long-term vacuum stability. Long-term outdoor exposure and climate-cycle tests can be used to assess changes in thermal performance and vacuum retention. Service-life expectations should be based on validated test data and the specified product construction.

8. Applications

With its slim profile, thermal insulation performance, acoustic benefits and resistance to internal condensation, vacuum insulated glass can be considered for a range of applications.

Buildings: Windows, doors, façades and skylights in residential, commercial and public buildings.

Transportation: Glazing for vehicles, high-speed trains and marine applications, subject to the relevant safety and performance requirements.

Refrigeration equipment: Doors and viewing panels for freezers, refrigerated display cabinets and other cooling equipment, where improved insulation can help reduce heat gain and frost formation.

Other applications: Agricultural greenhouses and building-integrated photovoltaic (BIPV) systems, where the glass configuration must be matched to the project’s thermal, structural, optical and safety requirements.

The appropriate product should be selected according to the intended application, required performance, glass configuration, safety classification and applicable standards.