How solar control glass coatings work

Solar control glass reduces the amount of heat and UV radiation that passes through a window, without blocking natural light. It is used in buildings, vehicles and optical applications where heat build-up is a problem. This article explains how the coatings work, which types exist and where they are applied.

What is solar control glass?

Solar control glass is glass that has been treated or coated to reduce solar heat gain. Without any coating, standard glass lets through a large portion of the infrared radiation in sunlight. This heats up the interior of a building or vehicle, which increases cooling costs and reduces comfort.

Solar control coatings change how the glass handles incoming solar energy. They can reflect, absorb or filter specific parts of the solar spectrum, particularly the near-infrared range between 700 and 2500 nm, while keeping visible light transmittance as high as possible.

The solar factor measures how much of the incoming solar energy ends up inside a building. It is also called the g-value or Solar Heat Gain Coefficient (SHGC). This includes energy that passes straight through the glass and energy that the glass absorbs and releases inward. The scale runs from 0 to 1. A lower SHGC means less solar energy enters the space. Solar control glass typically has an SHGC between 0.2 and 0.5, compared to 0.85 or higher for standard uncoated glass.

What do U-value and SHGC mean?

Two values describe how a glass unit handles heat. The U-value measures how easily heat passes through the glass because of the temperature difference between inside and outside. It is expressed in W/m²K, and a lower U-value means better insulation.

The SHGC measures solar heat, so it says nothing about insulation. According to the Whole Building Design Guide, a glass unit with an SHGC of 0.6 lets in twice as much solar heat as one with an SHGC of 0.3.

Solar control coatings mainly lower the SHGC. Low-e coatings also lower the U-value. Which value matters most depends on the climate, as the section on low emissivity glass explains.

How solar control coatings are applied

Solar control coatings are applied to the glass surface using two main methods: hard coat and soft coat.

Hard coat coatings are applied during glass production, while the glass is still hot. The coating bonds directly to the glass surface and is highly durable. Hard coat glass can be used as single pane glass and handled without special care.

Soft coat coatings are applied after the glass has cooled, using a vacuum deposition process. They offer better thermal performance and lower emissivity than hard coat options, but are more sensitive and need to be protected inside an insulated glass unit. Most high-performance low emissivity glass uses a soft coat process.

Low emissivity glass and solar control

Low emissivity glass, also known as low-e glass, is one of the most common types of solar control glazing. A low-e coating reduces the amount of infrared radiation that passes through the glass, which reduces heat transfer between inside and outside.

Low-e coatings work differently depending on the climate. In cold climates, low-e glass is designed to let in solar heat, while keeping interior heat from escaping. In hot climates, the priority is blocking solar heat gain while keeping the interior cool. Solar control low-e coatings are optimised for hot climates and high solar radiation environments.

Low e glass coating can be combined with other coatings to create dual reflective glass, which has different reflective properties on each side. This reduces glare while keeping visible light transmittance high.

Infrared absorbing nanoparticles in solar control glass

One approach to solar control coatings uses infrared absorbing nanoparticles dispersed in a thin film applied to the glass surface. Instead of reflecting near-infrared radiation, the nanoparticles absorb it and dissipate it as heat within the coating layer.

This approach has advantages for applications where reflection is undesirable. On a building facade, reflecting heat back toward people on the street is not always practical. An absorbing coating handles the heat within the glass itself.

Lanthanum hexaboride (LaB₆) nanoparticles absorb strongly in the 800 – 1400 nm near-infrared range at very low doses, between 10 and 100 mg per square metre. The coating stays visually transparent with only a slight greenish tint, because the absorption occurs in the infrared range, not the visible range. For more on how LaB₆ nanoparticles work as an infrared absorber, visit our LaB₆ nanoparticles page.

UV protection in solar control glass

Solar control glass also reduces UV transmission. UV radiation causes fading of furniture, flooring and textiles. Most solar control coatings block a significant portion of UV radiation, typically below 380 nm, while keeping visible light coming through.

This is particularly relevant in commercial buildings with large glazed facades, where interior materials are exposed to prolonged sun exposure. Solar control window film applied to existing glass is a cost-effective way to add UV protection without replacing the glass.

Where solar control glass is used

Buildings and architecture

Solar control glazing is standard in commercial buildings with large glass facades. It reduces cooling costs in hot climates and improves comfort near windows. Double glazed units with a solar control low-e coating on one of the inner surfaces are the most common solution in new construction.

Automotive glass

In vehicles, solar control coatings reduce heat build-up inside the cabin without darkening the windows. Automotive solar control window film is also widely used as an aftermarket solution for side and rear windows.

Insulated glass units

In insulated glass units, the solar control coating is placed on one of the inner glass surfaces, where it is protected from the outside environment. The position of the coating within the unit affects its thermal performance and SHGC.

Industrial and optical applications

Solar control coatings are also used on optical components, sensors and industrial glass where controlling which wavelengths pass through matters for the performance of the system.

Frequently asked questions about solar control glass

Summary

Solar control glass reduces solar heat gain, UV radiation and thermal discomfort without blocking natural light. Coatings are applied as hard coat or soft coat, with soft coat low-e coatings offering the best thermal performance. Infrared absorbing nanoparticles like LaB₆ offer an alternative approach for applications where reflection is not practical. Solar control glazing is used in buildings, vehicles and insulated glass units across hot and cold climates.