Low-e glass explained in plain English

What is low-e glass? Where and why is it used? In this article, we give you the facts without the jargon.



Spend long enough in the world of glass, and you're sure to come across references to low-e glass. So, what is it, how does it work and where and why is it used?

The "low-e" in "low-e glass" stands for "low-emissivity". Standard glass absorbs and radiates a lot of heat. Low-e glass reflects it while letting natural light pass through. This makes it more energy-efficient than standard annealed glass.

Emissivity measures the thermal energy emitted by a material. Matte black paint, for instance, has high emissivity while aluminium foil has low emissivity.

Ordinary glass has a high emissivity of around 0.84. Low-e glass combines the functionality of standard glass with low emissivity.

This is achieved by treating the glass with a microscopic and transparent metallic coating.

It's primarily used to reduce emissivity, reflecting rather than transmitting thermal energy. But it's also used for seasonal temperature control.

In winter, low-e glass reflects indoor heat back into the room. In summer, it deflects heat from the sun. This helps regulate the building's internal temperature.

It has the added benefit of blocking the most damaging ultraviolet (UV) and infrared rays.

What coatings does low-e glass use?

Low-e glass uses two main coatings: soft-coat (sputter-coated) and hard-coat (pyrolytic).

A soft-coat coating consists of multiple, super-thin layers. These contain silver or silver oxide.

Soft coatings are fragile and must be sealed within an insulated glass unit (IGU). They offer high thermal performance and low U-values.

Hard-coat or pyrolytic coatings, by contrast, use a fused layer of tin oxide applied to glass during manufacturing. These coatings are durable and can be used for exposed surfaces. That said, they tend to be less thermally efficient than soft-coat equivalents.

In modern windows, multiple layers of silver can be stacked with anti-reflective metal oxide layers such as titanium or zinc oxide. This helps balance solar heat gain reduction with optical clarity.

How does low-e glass work?

The microscopic and transparent metallic coatings on low-e glass reflect radiant heat rather than absorb it. This means greater control over heat retention all year round. At the same time, the coating is transparent, and daylight passes through as normal.

The coatings are super-thin layers of metallic oxides or silver. And when we say thin, we mean thin – thinner, believe it or not, than a human hair. These coatings lower the emissivity of the glass to somewhere between 0.02 and 0.05.

These coatings have been compared to a thermal mirror. They reflect heat back to its source rather than letting it escape through the glass.

This has obvious benefits for temperature regulation. In summer, solar heat can be reflected away from the building and in winter, indoor heat bounces back inside.

And while the coatings block heat and UV rays, there's one thing they don't block: light. That means you get all the benefits of daylighting without the downsides of high-emissivity glass.

Where is low-e glass used?

Low-e glass is widely used wherever improved thermal insulation is required. It's most commonly incorporated into double- or triple-glazed IGUs.

In the UK, low-e glass has become a standard feature of energy-efficient glazing. Building Regulations set thermal performance requirements for windows and doors. Incorporating a low-e coating is one of the main ways manufacturers reduce heat loss and achieve the required U-values.

For this reason, low-e glass is commonly used in residential windows and glazed doors. It can also be incorporated into roof windows, skylights and other overhead glazing, where good thermal performance is particularly important.

Low-e glazing can be useful throughout a building, including in colder or less sun-exposed rooms, because it helps retain heat by reducing radiant heat loss through the glass. However, low-e performance alone does not necessarily prevent summer overheating.

Where solar gain is also a concern – for example in large areas of glazing, roof glazing or highly glazed commercial façades – low-emissivity properties are often combined with solar-control glass.

This helps designers balance thermal insulation, daylight and protection against excessive solar heat gain.

What are the benefits of low-e glass?

There are five key benefits of using low-e glass.

1. Energy efficiency

The reflective nature of low-e glass enables it to block heat in summer and reflect heat back into a room in winter. This means it easily outperforms standard double glazing for energy efficiency.

2. Cost savings

Because insulation is improved, utility bills drop, with building occupants relying less on heating and cooling systems.

3. UV reduction

The coating on low-e glass blocks the vast majority of UV rays. This protects furniture, carpets and fabrics from fading.

4. Less condensation

Low-e glass can reduce condensation on windows. And with less risk of condensation, the possibility of mould is also significantly reduced.

5. Sustainability

Low-e glass helps lower the impact of buildings on the environment. That's why it's a core material for new and replacement windows.

What kinds of glass can be made low-e?

Pretty much any kind of glass can be made low-e – the manufacturer just needs to add the necessary coating.

Low-e products can begin life as standard float glass, tinted or patterned glass, laminated glass, toughened glass or heat-strengthened glass.

At ToughGlaze, we provide a wide range of glass products that are compatible with low-e coatings. All are cut, processed and shipped from our state-of-the-art facility in Bedford, UK.

Plus, with ClimaGuard® 365, we offer a high-performance low-e glass product that's supplied ready to use in a double- or triple-glazed IGU.

ClimaGuard® 365

ClimaGuard® 365 is a high-performance low-e glass that combines thermal insulation with solar control for windows and doors.

Designed for year-round comfort, it helps retain warmth in winter while reducing solar heat gain in summer. In the right application, it can leave rooms feeling up to 9°C cooler during hot weather.

That performance doesn't come at the expense of natural light. In its standard double-glazed configuration, ClimaGuard 365 achieves 75% visible light transmission, helping create a bright, neutral appearance while delivering a Ug value of 1.0 W/m²K.

Available in double- and triple-glazed IGUs, ClimaGuard 365 can be supplied as annealed, toughened, heat-strengthened or laminated glass to suit the application.

Looking for high-performance low-e glass for your next project? Get in touch with ToughGlaze for expert advice and a quick, competitive quote.