Low-E glass, short for Low-Emissivity glass, is a type of glass coated with an ultra-thin and transparent layer of metal oxides, almost invisible to the naked eye. This special coating reflects infrared and ultraviolet radiation while still allowing natural light to pass through, keeping interior spaces bright without the negative effects of heat or harmful radiation.
This technology helps maintain a stable indoor temperature year-round: in winter, the glass retains interior heat, while in summer, it prevents solar heat from entering. Besides enhancing comfort, Low-E glass significantly reduces energy costs, protects interior furnishings from fading due to UV rays, and contributes to the longevity of buildings.
Low-E glass is composed of a glass substrate (float glass) and a special ultra-thin metal oxide coating. Depending on the manufacturing method, this coating may be applied directly during the float glass production process or after the glass has been fabricated.
Usually clear float glass or tinted glass, with common thicknesses ranging from 5–19 mm. This provides the main mechanical strength of the glass.
Made of multiple ultra-thin layers of metal oxides (commonly silver, titanium oxide, zinc oxide), with a total thickness of only a few hundred nanometers.
The coating reduces thermal emissivity by blocking infrared and UV radiation while maintaining excellent visible light transmission.
Hard-Coat / On-line Low-E Glass:
The coating is applied directly during the float glass production process at very high temperatures. The coating is durable, resistant to scratching, and can be used on exterior surfaces. However, its thermal insulation performance is lower compared to soft-coat Low-E glass.
Specifically, during float glass production (silica sand, soda, lime, etc., melted at ~1,500°C and floated on a tin bath), a thin layer of metal oxides is sprayed onto the hot glass surface at around 600–700°C. This “on-line” coating becomes fused into the glass structure, creating a permanent, weather-resistant surface that does not peel off. It allows light transmission while reflecting infrared heat. Though less energy-efficient than soft-coat Low-E, its main advantages are durability and suitability for harsh outdoor conditions.
Soft-Coat / Off-line Low-E Glass:
Produced in a vacuum sputtering chamber using magnetron sputtering deposition. The coating delivers superior thermal insulation and heat reflection compared to hard-coat glass but is more delicate and usually requires installation within insulated glazing units (IGUs) for protection.
In this process, cleaned glass sheets are placed in multi-chamber vacuum coaters, where metal oxide particles are deposited onto the surface via cathode sputtering. This creates an ultra-thin, uniform, and tightly bonded coating that controls heat radiation while maintaining high transparency.
Single Silver Low-E: One silver layer, standard energy-saving performance.
Double Silver Low-E: Two silver layers, better thermal reflection and solar control.
Triple Silver Low-E: Three silver layers, maximum thermal insulation and light control, commonly used in modern high-performance buildings requiring optimal energy efficiency.
Low-E glass provides excellent insulation compared to ordinary glass. In insulated glazing units with inert gas filling, U-values can reach as low as 1.0–1.6 W/m²·K, minimizing heat loss and maintaining indoor temperature stability.
Depending on the type, Low-E glass can adjust solar radiation absorption and transmission. Typical SHGC values range from 0.23 to 0.37, balancing natural daylighting with reduced solar heat gain.
Thanks to its multi-layer structure and special coatings, Low-E glass reduces noise transmission more effectively than standard glass. When combined with insulated glazing and inert gases, soundproofing performance is further enhanced, ensuring quieter indoor spaces.
Low-E glass usually has an exterior reflectance of about 11–14%. This maintains a natural appearance, avoids glare, and enhances building aesthetics.
[1] Guardian Glass, Low-Emissivity Glass (Low-E Glass). Guardian Glass. Accessed: Aug. 22, 2025. [Online]. Available: https://www.guardianglass.com/ap/en/our-glass/glass-types/low-e-glass
[2] Guardian Glass, Low-E Coatings and Energy Performance. Guardian Glass. Accessed: Aug. 22, 2025. [Online]. Available: https://www.guardianglass.com/ap/en/our-glass/glass-types/low-e-glass
[3] Efficient Windows Collaborative, Types of Low-E Glass. Efficient Windows. Accessed: Aug. 22, 2025. [Online]. Available: https://efficientwindows.org/gtypes-2lowe/
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Low-E glass is coated with an ultra-thin, nearly invisible layer of metal oxide that works “intelligently” to control heat radiation. It allows natural day){kind=link}