Modern buildings demand more from their glazing than ever before. Whether it’s improving energy efficiency, reducing heat loss, enhancing sound insulation or creating more comfortable living spaces, insulated glass units (IGUs) have become the standard solution for residential and commercial glazing.
From double glazed windows and doors to rooflights and large-scale façades, IGUs play a vital role in improving thermal performance while allowing natural light to flood into buildings. But what is an insulated glass unit (IGU), how does it work, and why is it so effective?
In this guide, we’ll explore everything you need to know about insulated glass units, including their components, benefits, performance ratings and applications.
What Is an Insulated Glass Unit (IGU)?
An insulated glass unit (IGU) is a glazing system consisting of two or more glass panes that are hermetically sealed together to create a single unit. The glass panes are separated by a spacer and filled with air or insulating gas, such as argon or krypton, creating an enclosed air space that significantly reduces heat transfer between the interior and exterior of a building.
A standard glass unit IGU is made up of:
- Two or more glass panes
- A perimeter spacer bar
- A sealed air or gas-filled cavity
- A primary seal
- Durable secondary sealants
- Optional low E glass coatings
These components work together to create a highly efficient glazing system that improves comfort, reduces energy consumption and enhances building performance.
How Does an IGU Work?
To understand the benefits of a glass unit, it’s important to understand how heat moves through a building.
Heat naturally travels from warmer areas to cooler areas. In properties fitted with single pane glass, warmth can easily escape through the glass surface, causing higher heating costs and reduced comfort during cold weather and the cold winter months.
An insulated glass unit slows this process by trapping a layer of air or gas between the panes. This insulating layer reduces thermal conductance and limits heat transfer through the glazing.
Unlike single glazing, where heat passes directly through one pane, a double glazed IGU creates a barrier that helps:
- Reduce heat loss
- Improve thermal comfort
- Lower energy bills
- Maintain more stable indoor temperatures
- Minimise condensation
The result is a building that stays warmer in winter, cooler in summer and more comfortable all year round.
The Main Components of Insulating Glass Units
Glass Panes
IGUs consist of multiple glass panes, typically two glass panes in double glazing or three panes in triple glazing.
The panes may be manufactured using:
- Standard float glass
- Laminated or tempered glass
- Acoustic glass
- Solar control glass
- Low E glass
Different glass thickness combinations can be used depending on the project requirements.
Gas Fill
Many high-performance IGUs feature a gas fill rather than ordinary air.
The most common options include:
Argon Gas
Argon is an affordable inert gas and the most widely used option in modern IGUs. As a noble gas, it is denser than air and helps reduce heat movement between panes.
Using approximately 90% argon gas can improve a unit’s U-value by up to 16% compared with air-filled units.
Krypton Gas
Krypton provides even greater insulation performance.
Although more expensive, krypton can improve a glazing unit’s U-value by up to 27%, making it particularly useful in premium and high-performance building projects.
Primary Seal and Secondary Sealants
Every IGU relies on high-quality seals to remain hermetically sealed.
The primary seal prevents moisture ingress and gas leakage, while the secondary sealants provide structural strength and durability.
Together, these seals help maintain long-term performance and prevent condensation forming within the cavity.
What Is Low E Glass?
One of the most significant advances in glazing technology has been the introduction of low E glass.
The term “Low E” stands for low emissivity. A microscopic metallic coating is applied to one of the glass surfaces to reflect infrared heat while still allowing visible light to pass through.
Modern low emissivity coatings help to:
- Reflect interior heat back into the room
- Improve energy efficiency
- Reduce heating costs
- Enhance indoor comfort
- Help control solar gain
A low E IGU provides substantially better thermal performance than standard glazing.
When looking at an IGU, there are often four surfaces within a typical double-glazed unit. The Low E coating is strategically positioned on one of these surfaces to maximise efficiency.
Understanding U-Values
When selecting double glazed units, understanding performance ratings is essential.
The U-value measures heat transfer in W/m²°C. In simple terms, it measures how much heat passes through a building element such as a window.
Lower U-values indicate better insulation performance. Modern IGUs can achieve U-values as low as:
- 1.0 W/m² for many high-performance double glazed windows
- Even lower values for triple glazing systems
Because less heat escapes through the glazing, lower U-values contribute directly to energy savings.
Energy Efficiency Benefits of IGUs
One of the biggest advantages of insulating glass units is improved energy efficiency.
Modern IGUs:
- Reduce heat loss during winter
- Reduce unwanted heat gain during summer
- Improve building energy ratings
- Lower heating and cooling costs
- Support sustainable construction
As building regulations continue to tighten, IGUs have become a key component in energy-efficient and environmentally responsible building design.
For homeowners, this means lower energy bills. For commercial properties, it can result in substantial long-term operational savings.
Sound Insulation and Acoustic Performance
In addition to thermal benefits, IGUs also deliver excellent sound insulation.
The combination of multiple glass layers and an insulated cavity helps reduce external noise transmission. For projects requiring enhanced acoustic performance, manufacturers may specify:
- Laminated glass
- Thicker glass
- Asymmetric glazing configurations
- Panes with different thicknesses
These solutions help dampen sound waves and can significantly improve indoor comfort in urban areas, near airports or alongside busy roads.
Compared with single pane glass, IGUs provide dramatically better acoustic performance.
Reducing Condensation
Condensation is a common issue associated with poor-performing glazing.
Because IGUs keep the internal glass surface closer to room temperature, they help prevent moisture from forming on interior surfaces.
This creates healthier internal environments while helping protect surrounding finishes from moisture damage.
Common Applications for Insulated Glass Units
Today, IGUs are found throughout the built environment.
Residential Buildings
Common applications include:
- Double pane windows
- Patio doors
- Sliding doors
- Rooflights
- Entrance doors
Commercial Buildings
IGUs are widely used in:
- Office developments
- Retail units
- Educational buildings
- Healthcare facilities
- Hotels
High-Rise Buildings
Modern façades rely heavily on high-performance glass panels and IGUs to deliver energy efficiency while maximising natural light.
Why IGUs Are Essential for Modern Buildings
Whether installed in windows, rooflights or curtain walling systems, insulated glass units keep homes warmer in winter and cooler in summer.
By combining multiple glass panels, specialised glass coatings, insulating gases and advanced sealing technologies, IGUs deliver exceptional levels of comfort and efficiency.
For architects, developers and homeowners alike, understanding what an insulated glass unit (IGU) is can help inform smarter glazing choices and improve long-term building performance.
Conclusion
An insulated glass unit (IGU) is a highly engineered glazing solution designed to maximise insulation, reduce heat loss, improve sound insulation and enhance overall building performance.
Featuring glass panes separated by a spacer, a sealed air space or gas fill, and advanced low E coatings, modern IGUs form the foundation of energy-efficient glazing systems. Whether filled with argon gas, krypton or air, these units dramatically outperform traditional single pane glass and help reduce energy consumption throughout the year.
At UKO Glass, our high-performance glazing solutions are designed to combine outstanding thermal efficiency, exceptional daylight transmission and long-term durability, helping create brighter, more comfortable and more sustainable buildings. Get in touch today to find out more!