Insulated Glass Configuration Guide: How to Choose Glass Thickness, Spacer Width, Gas Filling and Low-E Options

Introduction

Choosing the right insulated glass unit (IGU) configuration is one of the most important decisions in modern building projects. The selected IGU structure directly affects thermal performance, indoor comfort, acoustic performance, safety, and long-term operating costs.

An improperly specified IGU configuration can result in increased energy consumption, condensation issues, or reduced service life. In contrast, the right combination of glass thickness, spacer width, gas filling, and Low-E coating can significantly enhance building performance while helping projects meet local energy requirements.

In this guide, we explain the key factors behind insulated glass selection, including glass thickness, cavity width, gas options, and Low-E combinations, helping architects, contractors, and buyers choose the most suitable IGU solution for their projects.

What Makes Up an Insulated Glass Unit (IGU)

Before selecting the right insulated glass configuration, it is important to understand the basic structure of an insulated glass unit (IGU). An IGU is not simply two pieces of glass placed together, but a carefully engineered glazing system designed to improve thermal insulation, acoustic performance and overall building comfort.

A typical insulated glass unit consists of several key components:

• Two or more glass panes that form the outer and inner layers of the glazing system.

• A spacer system (such as aluminum, warm-edge stainless steel or foam spacers) that maintains the distance between glass panes and creates the insulating cavity.

• Primary and secondary seals that help maintain the airtight structure and prevent moisture from entering the cavity.

• Desiccant material inside the spacer to absorb residual moisture and reduce condensation risks.

• Optional gas filling, such as air, argon or krypton, to further improve thermal performance.

An IGU consists of multiple components, including glass panes, spacer, sealant layers and an insulating cavity filled with air or gas. Each element plays an important role in maintaining energy efficiency and long-term durability.

The sealed cavity between glass panes is the core feature that gives IGUs better thermal and acoustic performance compared with single glazing. By combining different glass types, cavity widths, gas fillings and coatings, IGU configurations can be customized to meet specific project requirements.

For a more detailed overview of insulated glass structure, components and common types, please refer to our article: What Is Insulated Glass?

Understanding Insulated Glass Configurations: What Do the Numbers Mean?

Insulated glass unit (IGU) configurations are commonly described by indicating the glass thickness, cavity width and additional performance features, such as gas filling, glass treatment or Low-E coatings. These specifications provide important information that helps define the overall performance characteristics of an IGU. By understanding these configuration details, architects, contractors and buyers can better compare different glazing options and select a solution that matches the requirements of their projects.

For example, a configuration written as 5+12A+5 typically indicates:

• The first 5 represents the thickness of the first glass pane (5mm).

• 12A represents a 12mm air-filled cavity between the two glass panes.

• The second 5 represents the thickness of the second glass pane (5mm).

The sealed cavity between the glass panes creates an insulating layer that helps improve thermal performance compared with single glazing.

In addition to glass thickness and cavity width, IGU configurations may also include different glass types, gas fillings and coatings to achieve specific performance requirements.

• Tempered glass (T) is used to improve mechanical strength and safety performance.

• Argon gas filling (Ar) helps reduce heat transfer through the cavity and improve thermal insulation.

• Low-E coatings help reduce radiant heat transfer and improve thermal and solar control performance.

For example, a higher-performance IGU configuration such as 6T Low-E + 16Ar + 6T combines tempered glass, an argon-filled cavity and a Low-E coating to achieve enhanced thermal and solar-control performance compared with conventional clear double glazing.

The main advantages of this type of configuration include:

• Improved Energy Efficiency:
  The Low-E coating helps reduce heat transfer, while the argon-filled cavity improves thermal insulation performance. Together, these features can help maintain more stable indoor temperatures and reduce heating and cooling loads.

• Enhanced Safety and Strength:
  Tempered glass provides increased mechanical strength and improved safety performance, making it suitable for applications where enhanced strength and safety are required.

• Improved Indoor Comfort:
  Improved thermal insulation and, depending on the Low-E specification, solar-control performance can help manage heat gain and visible light, contributing to a more comfortable indoor environment.

Depending on the project requirements, similar high-performance IGU configurations may be used in commercial buildings, curtain walls, high-end residential projects, large windows, glass doors and skylights, where thermal performance, safety and occupant comfort are important considerations.

How Does Glass Thickness Affect Insulated Glass Performance?

The glass thickness in an insulated glass configuration is mainly selected based on the size of the glazing panel, structural requirements, safety considerations and the expected level of performance.

A thicker glass pane is typically considered when a project requires higher load resistance, larger glass sizes or improved safety performance. However, the optimal thickness depends on the complete glazing system rather than thickness alone.

The following examples show how different glass thickness combinations are commonly selected for various applications:

Our insulated glass units are available in a wide range of configurations, including different glass thicknesses, cavity widths, Low-E options and gas fillings to meet different project requirements. Share your project details with us, and our team can help recommend the most suitable IGU configuration for your application.

How Do Spacer Width and Gas Filling Affect IGU Performance?

The space between glass panes is one of the key elements that determines the thermal performance of an insulated glass unit (IGU). Both the cavity width created by the spacer system and the gas filling inside the cavity influence how effectively the glazing system reduces heat transfer.

Spacer Width: Why Does the Cavity Size Matter?

The spacer system maintains the distance between glass panes and creates the insulating cavity inside an IGU. Common cavity widths include 9mm, 12mm, 16mm and 20mm, with the selection depending on the required thermal performance and overall glass configuration.

A wider cavity can improve insulation performance by providing more space for insulating gas. However, an excessively wide cavity may increase gas movement and convection within the sealed space, limiting further thermal improvement.

The optimal cavity width depends on factors such as:

• Gas filling type (air or argon)

• Glass configuration

• Low-E coating selection

• Project insulation requirements

Besides cavity width, the spacer material also affects the overall performance of an insulated glass unit, especially around the glass edges. Different spacer options are available depending on project requirements:

Aluminum Spacer Bar: Traditional spacer solution widely used in standard IGU applications	Warm Edge Spacer: Designed to reduce heat transfer at the glass edge	4SG Warm Edge Spacer: Advanced warm edge system with enhanced sealing performance

Gas Filling: Why Does the Choice of Gas Matter?

The gas inside the insulated glass cavity plays an important role in reducing heat transfer and improving the thermal performance of an IGU. While standard units may use air-filled cavities, higher-performance configurations often use inert gases such as argon or krypton to enhance insulation.

Common gas filling options include:

• Air: Standard cavity filling option with reliable performance and cost efficiency.

• Argon: The most commonly used upgrade option, helping reduce heat transfer and improve thermal insulation.

• Krypton: Higher-performance gas with lower thermal conductivity, suitable for narrower cavities where space is limited.

How Does Low-E Coating Improve Insulated Glass Performance?

Low-E (Low Emissivity) coating is one of the most commonly selected performance options for high-performance insulated glass units (IGUs). Applied as a microscopically thin functional layer on the glass surface, the Low-E coating helps reduce radiant heat transfer while maintaining good natural light transmission.

A Low-E (Low-Emissivity) coating is a microscopically thin functional layer applied to the glass surface to improve energy efficiency in modern glazing systems. It helps reduce radiant heat transfer while maintaining good visible light transmission, improving thermal comfort and solar control when used in insulated glass units.

Low-E Glass Coating Options

Different Low-E coating options can be selected according to the required balance between thermal insulation, solar control and daylight transmission.

At Reach Building, our Low-E glass solutions are available with different coating options, including Single Silver, Double Silver and Triple Silver, allowing glazing systems to be customized for different climate conditions, building designs and energy performance requirements.

The selection of the appropriate Low-E coating depends on factors such as local climate, building orientation, window size and the desired level of solar control and thermal insulation.

Key Benefits of Low-E Glass in IGU Applications

• Improved Thermal Insulation: Low-E coatings help reduce heat transfer through the glazing system, improving insulation performance in different climate conditions.

• Solar Heat Control: Low-E glass helps reduce unwanted solar heat gain while maintaining good visible light transmission, supporting a more comfortable indoor environment.

• Energy Efficiency: By improving the thermal performance of IGUs, Low-E glass can help reduce heating and cooling requirements and support lower building operating costs.

• Enhanced Indoor Comfort: Better control of heat transfer helps maintain more stable indoor temperatures, especially in buildings with large glazed areas.

A Low-E insulated glass unit combines coated glass, spacer systems and sealed air or gas cavities to achieve improved insulation and solar control performance. It boosts energy efficiency (low U-value: 1.60-1.84 W/m²K), reduces heat gain/loss, blocks 99% UV rays, and enhances sound insulation (STC 40-50).

While Low-E glass and insulated glass are often used together in modern glazing systems, they serve different functions. Low-E glass focuses on controlling radiant heat transfer through a coated glass surface, while insulated glass improves thermal performance through a sealed multi-pane structure.

For a detailed comparison between these two glazing solutions, please refer to our article: What Is The Difference Between Low-E Glass And Insulated Glass?

Common Types of Insulated Glass Unit (IGU) Configurations

Insulated glass units are available in several configurations based on the number of glass panes, cavity structure and performance requirements. Common options include double glazing, triple glazing, vacuum insulated glass and customized hybrid solutions.

Double Glazing: Balanced thermal insulation, acoustic performance and cost efficiency	Triple Glazing: Enhanced thermal insulation and improved acoustic performance	Vacuum Insulated Glass (VIG): Excellent thermal insulation with a slim profile and reduced condensation risk

Conclusion

Choosing the right insulated glass configuration depends on your project requirements, including thermal performance, solar control, safety and energy efficiency. At Reach Building, we provide customized insulated glass solutions with flexible options for glass types, coatings, spacer systems and configurations. Share your project requirements with our team, and we can recommend a suitable IGU solution for your application.