Low-E Glass Explained

Published September 24, 2021
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Low E coatings are also known as Low-E glass. This is a popular building material that was developed to limit the rays of ultraviolet and infrared light that normally pass through glass. Low-E glass is also popular because it blocks UV rays without compromising the amount of visible light being transmitted.

What is Low-E Glass?

How a material radiates energy is known as emissivity. The E in Low-E stands for “low emissivity” – which is measured on a scale from 0.00 to 1.0. A Low-E coating on windows is done by applying multiple invisible layers of metallic oxide. The Low-E coating allows natural light to enter your home or office space while deflecting potentially harmful UV rays and infrared light back out into the natural environment. A Low-E coating is applied in microscopically thin and transparent layers to minimize heat transfer, increase visible light transmittance all while increasing energy efficiency. Generally speaking, higher reflective materials have a low emissivity while dull and darker colored materials have a higher emissivity. For more information about emissivity ratings, Low-E glass, or E-glass coatings, call a professional like Lake Washington Windows and Doors. They know how to help you decide what window glass surfaces offer the best solar heat gain coefficient.

What does Low-E glass do?

Uv light, visible light, and infrared are all part of the solar energy spectrum. Low E-glass reflects infrared light and UV light leaving you with a more energy-efficient window. Low E-glass acts as a multi-layer insulating glass unit that regulates which parts of the solar spectrum are allowed to enter a room. Some of the benefits of using Low E coatings are below:

  • Durability. Low-E coatings cannot be scratched off, wiped off, or damaged because the coating is applied to the inside part of the glass.
  • Significant reduction in heat loss. Eliminate heat transfer and reduce heat loss in your home by as much as 50%.
  • Cost Savings. Residential homeowners often see a reduction in energy bills by using low-E coatings
  • Protection of household items. UV light rays are prevented from penetrating and damaging furniture, couches, curtains, flooring material, and other upholstery.

Summer Time

When you replace your windows and use a low emissivity material like low-E glass in the summertime, you can have better control over solar heat gain. Especially during the hours of direct sunlight. Since it has a lower (SHGC), or solar heat gain coefficient, a lesser amount of solar heat is transferred to your interior. This helps maintain cooler and comfortable temperatures.

Winter Time

Passive low-e coatings are ideal in very cold climates because the sun’s short-wave infrared energy still flows through and helps heat your home when it’s cold outside, all while reflecting the interior long-wave heat energy back inside your home.

Is Low-E glass worth the money?

Yes! Low-E glass is worth the investment. E glass costs few dollars more than standard glass, but in return, you get energy savings, improved year-round comfort, and enhanced environmental protection. Additionally, that nominal extra cost will pay for itself with the money saved on utility bills!

Energy Efficiency

Low-E glass helps reduce energy costs by reducing the heat that leaves and enters your home. During the summer low-E glass blocks hot air from entering the home. While in the winter, low-E glass captures warm air inside the home which will reduce the burden on a furnace. Heat loss (or heat gain) through windows occurs by three methods.

  • Radiant heat – When heat flows via absorption, then re-radiated through the new surface (like touching a hot glass surface).
  • Convection heat – When heat flows via air movement (like roasting a marshmallow).
  • Conduction Heat – When heat is transferred directly through materials via contact (like boiling water or grilling a steak.

Upgrading your glass surfaces improves energy efficiency because you control the heat gain coefficient.

Resale Value

Typically, homebuyers get impressed by a beautifully updated kitchen or enchanting immersive bathroom, but nowadays, a set of good windows is also a major priority. Recent studies done by Remodeling Magazine show that a new set of energy-efficient windows returns up to 75% of the money you invested.

UV Protection

Using a mechanism similar to the one used for thermal radiation reflection, low E windows prevent the majority of UV radiation from entering a home. Because of this, a Low E window coating resists ultraviolet light and prevents harmful UV exposure from damaging draperies, carpets, sofas, and other furniture.

High Visible Light Transmission

Visible transmittance or VT is expressed as a number from 0 to 1. The larger the number, the more light will be visible. It is also known as Visible light transmission or VLT which is expressed as a percentage %. VT measures the amount of light entering in the visible portion of the solar light spectrum as it passes through glass. Example:

  • VT .6 would be VLT 60% of the light is visible
  • VT .93 would be VLT 93% of the light is visible

Are there different types of Low-E glass?

There are two different types of energy-efficient Low E-glass: passive Low-E coatings, and solar control Low-E coatings. Both solar control and passive Low-E glass can be made through either a hard coat or soft coat process.

Hard Coating

A hard-coated Low-E glass window is manufactured through the pyrolytic process. This method is done by applying a thin layer of molten metal to the sheet of glass during the manufacturing process, while the glass is near molten. The heat bonds the metal to the glass, creating an almost inseparable “hard” coating.

Soft Coating

A soft-coated Low-E glass window is manufactured through the MVSD process. The  Magnetron Sputter Vacuum Deposition method means the particles that make up the metal Low E layer are applied to pre-cut panes of glass, at room temperature. The particles of metal are applied in a vacuum-sealed chamber while filled with an inert electrically charged gas. The final metal coating is extremely thin, fairly delicate, and “soft”.

Top Brands for Low-E Glass Windows

The glass industry is controlled by three cutting-edge manufacturers, Milgard, Anderson, and Provia. These three companies supply Low E windows to the majority of window installation companies that use high-performing glass bundles.


SunCoat Low-E2 glass comes standard on all Milgard dual-pane windows and SunCoast products are Energy Star rebate eligible. Milgard also offers upgraded Low E products like SunCoatMAX, which is considered to be Low E3. Milgard windows have the best clarity and highest performance of all solar gain Low-E glass. Some of the benefits of using Milgard are below:

  • Increases glass temperature in winter
  • Lowers solar heat gain more than two-coat, Low-E glass in the summer
  • Provides an ultraviolet light barrier to protect UV-A and UV-B rays from damaging your fabrics and other furnishings


Are you are looking to control cooling costs, increase natural light, or just want something that controls long-wave infrared energy? If so, look at ProVia’s Aeris, Endure, and Aspect window lines. All ProVia Aeris, Endure, and Aspect windows include ComforTech Warm Edge Glazing System, featuring Super Spacer Reverse Dual Seal Technology, that reduces heat loss, interior condensation, and guarantees warmer glass temperatures.

Low-E Glass Upgrades

Upgrading your window glass surfaces improves living conditions and adds value to your home. Low E windows also lower your air conditioning and improve energy efficiency. Furthermore, Low-E glass upgrades prevent incident solar radiation and allow you to control thermal energy.

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Written by Lake Washington Windows

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