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Everything You Need to Know About Low-e Glass

Cutting down on household expenses is one of the many ways a person can save money. Luckily, there are a bunch of home improvement projects that can prevent energy loss and help you save money in the long run. If you’re concerned about skyrocketing heat and cooling bills due to changing weather, then you might want to invest in installing Low-e glass into your windows.

Energy efficient homes have dual-pane, low e glass windows

What is Low-e Glass?

When the air inside of your home escapes outside, or cold drafts and desert winds enter your home, your air conditioning and heaters will have to run more to keep your house at a consistent temperature. This can really drive up your energy bills.

Your windows in particular are susceptible to large amounts of energy loss. While experts estimate that 70% of all energy loss is due to poorly insulated doors and windows, 90% of window heat loss is through the window glass. If you live in a cold climate, the wrong type of glass will let heat escape outside. However, if you live in a warm environment, infrared and ultraviolet light will enter through the glass and not only heat-up your house, but also fade your upholstery and wall trimmings.

So, what is low e glass? Low-e, or “low emissivity” glass, is the energy-efficient solution to this problem. It has a microscopically thin metallic oxide coating. It’s transparent and heat-reflective to minimize the amount of infrared and ultraviolet light entering into your home without blocking natural light. It keeps heat from entering your home during the summer and keeps heat circulating inside your house during the winter.

To simplify, Low-e glass works just like your favorite thermos. If you have hot coffee, it will reflect the heat of your drink to keep it constantly warm. If you have ice-cold water, it’ll reflect the cold to keep your ice from melting. And it does all this while keeping outside temperatures out. Low-e glass doors will help maintain the temperature of your house while keeping cold and heat out.

What is low-e glass? How can you tell if you have low e glass?

What Are the Types Low-E Glass

There are two types of Low-e glass: hard-coat and soft-coat. Both low-e glass door options are energy efficient, but hard-coat glass (also known as passive control) had its metallic oxide coating added during production, making it hard to scratch. Soft-coat Low-e glass (also known as solar control) is applied after the glass is made, making it more delicate. Generally, both hard-coat and soft-coat Low-e glass are effective, but soft-coat has a higher thermal resistance value (R-value), meaning it is better at heat insulation.

There are a few more factors used to measure the effectiveness of Low-E glass:

  • Solar Heat Gain Coefficient (SHGC): Measures how much solar radiation is admitted through a window and is either absorbed or released as heat inside the house. The lower the SHGC, the less heat the glass transmits and the great its shading ability.
  • U-Value: How well the window is insulated. The lower the U-value, the better the window helps to retain heat.
  • Visible Light Transmittance (VLT): How much visible light passes through the glass. The higher the VLT, the more visible light is transmitted.
  • Light to Solar Gain (LSG): Measures how well a window lets in natural light while blocking heat. The higher the LSG is, the more light comes through the window without excess heat.

Endura Flap patio panel inserts are made to be well-insulated against extreme weather conditions

Does Endura Flap Use Low-e Glass?

We know that not every pet door out there does well in extreme weather conditions. Most are not well-insulated, the flaps are easily damaged and do not seal, and sliding glass door inserts do not protect against cold drafts.

When making our sliding glass inserts, we made sure that our pet door has the greatest energy efficiency value out there. Not only do our flaps have an airtight magnetic seal and our frames are lined with insulating weatherstripping, but the glass we use in the majority of our sliding door and window panels has a Low-e coating.

Check out our performance measurements:

Solar Heat Gain Coefficient 0.8
U-Value 0.44 Btu/h·ft2·F (United States)

2.49 W/m2·K (International)

Visible Light Transmittance 77%
Ultraviolet Light Transmittance 52%
Light to Solar Gain 1.11

Endura Flap for Sliding Glass Pet Doors are the most energy-efficient dog doors on the market. With their Low-e glass, they’re guaranteed to help reduce energy cost and reduce destructive UV rays from fading your furniture and art while sitting letting natural light into your home. 

This panel and window kit has everything you need to keep your pet door secure.

Can't decide which panel you need? Read about the differences between vinyl and aluminum pet door panels here. 

If Low-e Glass sounds right for you, then check out some of our best Endura Flap pet doors with Low-E glass:

The Endura Flap Thermo Panel 3e in colors white, brushed aluminum, and bronze

Endura Flap Thermo Panel 3e

White vinyl frame sliding glass door insert panel from Endura Flap

Endura Flap Vinyl Sliding Glass Dog Door

The white frame and clear flap thermo sash 3e cat door for sash windows

ThermoSash 3e Pet Door for Sash Windows

How to Tell if Glass is Low-E?

You might be curious now how to tell if glass is low e. If you want to check whether or not your current windows or sliding doors are Low-E there are a few things you can look for: 

  • Hold a lit match or a pen light up in front of the window or siding door. In dual-pane glass, you will see four reflections of the flame due to the four glass surfaces of the glass unit.
  • If the window or slider contains low-e glass, one of the reflections will be a different color (slightly more translucent) than the rest of the images.
  • If the window does not have low-e glass, the four reflections of the flame or light will be the same color.


Elizabeth Muenzen

Written by

Content Specialist

Pets: My dog Benji is mixed Yorkie, Poodle, Chihuahua, and MaltiPom (YorkiPooChiMaltiPom?), yet he mysteriously bears no resemblance to any of these breeds.
Fun stuff: I love to cook!

Content Specialist

Pets: My dog Benji is mixed Yorkie, Poodle, Chihuahua, and MaltiPom (YorkiPooChiMaltiPom?), yet he mysteriously bears no resemblance to any of these breeds.
Fun stuff: I love to cook!

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