The first insulating glass unit (IGU)—a double-glazed window—was patented in the U.S. in 1865 by inventor Thomas Stetson. Since then, insulating glass technology has advanced dramatically, driven by growing demand for improved energy efficiency in buildings.

Today, a wide range of innovative insulating glass solutions is available, from smart glass to triple glazing, advanced coatings, and vacuum-insulated glass (VIG). Let’s explore the evolving landscape of insulating glass, how it impacts building performance, and why it matters.

What is Insulating Glass?

At its core, insulating glass consists of double- or triple-glazed units—two or three panes of glass separated by a sealed air or gas-filled space. This construction minimizes thermal transfer, reducing the flow of heat and cold through a building envelope and improving energy performance.

As energy efficiency requirements tighten, manufacturers are developing advanced insulating glass technologies to meet evolving performance standards and support sustainable building design.

How Is Thermal Efficiency in Glazing Measured?

Thermal efficiency in glass is typically measured using two key metrics:

• U-value (also known as U-factor): This indicates the rate of heat transfer through the glass. The lower the U-value, the better the insulating performance. U-value is expressed as the amount of heat (in BTUs) that passes through one square foot of glazing per hour for every degree of temperature difference.
• R-value: This measures thermal resistance. The higher the R-value, the greater the material’s insulating properties. While R-value is often used for materials like walls and roofs, it can also help assess the insulating performance of glazing products.

It’s also important to consider the embodied carbon of building products. Some insulating glass technologies are more carbon-intensive to produce than others. Embodied carbon is typically measured in terms of Global Warming Potential (GWP), expressed as kilograms of carbon dioxide equivalent per metric ton of material.

How Does Technology Improve Glazing Performance?

Innovative insulating glass technologies can dramatically improve thermal performance. For example, a comparison of U-values across common glazing configurations shows significant advancements, according to Building Design + Construction.

New Types of Insulating Glass

While traditional types of insulating glass including double- or triple-pane insulating glass units (IGUs) with argon or krypton gas have been around for decades, a range of newer types of insulating glazing technology have recently come online.

Smart Glass:
Also known as switchable glass, smart glass dynamically adjusts its transparency, opacity, or color in response to external stimuli—such as light, heat, or electricity—helping control solar heat gain and improve privacy.

Types of smart glass include:

• Electrochromic: Changes tint when an electric current is applied

• Thermochromic: Reacts to temperature fluctuations

• Photochromic: Adjusts to light conditions

Fourth-Surface Low-E Coatings:
This innovation applies energy-efficient coatings to all four surfaces of a double-pane IGU, maximizing thermal performance without sacrificing natural light. Fourth-surface Low-E glass improves U-values compared to traditional configurations.

Vacuum Insulating Glass (VIG):
While VIG has been around in one form or another since the early 1900s, and is relatively common in Asia and Europe, it has only recently become more popular in North America. As mentioned in the table above, VIG can improve U-values by as much as 80 percent over a traditional dual-pane, Low-E glass IGU.

VIG is different from argon- or krypton-filled double glazed units in that it creates a vacuum between the glass panes, forming a barrier that virtually eliminates heat transfer and results in lower U-values and higher R-values.

According to Glassforum.org, “VIG units with a Low-E coating can have R-values up to R-20, offering thermal capabilities five times better than conventional insulating glass and up to 20 times better than monolithic glass.” VIG can also reduce the chances of condensation in the window.

Solar/Photovoltaic Glass:
This technology integrates photovoltaic (PV) cells into the glass, allowing windows to generate electricity while maintaining transparency. PV glass uses silicon semiconductors between conductive layers, offering an innovative way to combine energy generation with building envelope performance.

Unicel Architectural’s Vision Control® IGUs

At Unicel Architectural, we’ve been at the forefront of insulating glass innovation for decades. Our Vision Control® IGUs offer precise control over light, sound, and privacy—available in double- or triple-glazed configurations with a range of energy-efficient options, including Low-E glass and glass-clad polycarbonate.

Contact Unicel Architectural today to learn more about how our insulating glass solutions can improve energy performance, comfort, and sustainability in your next project.