The Lowdown on Low E Glass

LowE Glass

As we write this blog, it’s July 2017 and we’re in Arizona. There may never be a better time to tell you what’s great about Low-E glass.


We’ll start at the beginning, though, and tell you what it is, first.


Low-E (low emissivity) glass is (typically double-paned) glass that’s been coated with metal oxides (using one of two methods) so that it reflects solar heat and only allows a small fraction of it into your home, while still letting in plenty of daylight.


The first method, pyrolytic, produces a passive or Hard-Coat Low-E and involves bonding a metallic oxide with the glass while it’s still in a semi-molten state. The coating is so strong and durable that it’s able to be used occasionally in single-pane applications.


Hard-Coat Low-E glass is recommended for cooler climates, though, because it lets in more of the sun’s warming infrared rays than does Soft-Coat Low-E. So that’s probably all the time we need to waste on that, then . . .


Let’s get to the good stuff: Soft-Coat Low-E!

Seriously, if you’re tired of shockingly high energy bills, overworking your poor cooling unit, tinted glass that gets hot/cracks, faded carpet/furniture or just plain being uncomfortable, you’re going to want to keep reading.


1. How it’s made: Soft-Coat Low-E is produced in a room-temperature vacuum through a process called Magnetron Sputtering Vapor Deposition (yeah, really), where multiple layers of metals, metal oxides, and metal nitrides are sprayed on pre-cut glass.


Because Soft-Coat is more delicate, it needs to be sealed in insulated glass. But while it may not beat Hard-Coat in toughness, Soft-Coat’s the hands-down winner in efficiency and solar control.


2.  What it does: When we talk about emissivity, we’re talking about a material’s ability to radiate energy. So glass that has low emissivity radiates far less solar energy into a home than ordinary glass. How much less?


Well, standard clear glass windows emit roughly 84% of the sun’s radiant energy into the home, whereas Low-E glass emits as little as 18%, while reflecting the other 82% back outside where it belongs.

3. Why it’s better than tinted glass: Tinted glass does more absorbing of radiant energy than reflecting, so the glass itself can get hot, therefore radiating more heat into a room than Low-E glass. And because it retains heat, tinted glass is prone to stress and breakage.


But not all Low-E glass windows are created equal.

Which is why XO Windows offers LoĒ³-340 by Cardinal. Check it out:


  • LoĒ³-340 blocks approximately 98% of harmful UV radiation. We don’t like UV rays because they’ve been proven harmful and are linked to skin damage, skin cancer, glaucoma, immunity issues, etc. And, they’re the ones responsible for bleaching out your carpets and furnishings!

  • LoĒ³-340 reflects nearly all of the invisible solar infrared rays. We don’t like infrared rays because they are the ones that make us hot. Oh, so miserably hot.

  • LoĒ³-340 has a Solar Heat Gain Coefficient (SHGC) of just 0.18. Very simply put, SHGC is the amount of solar heat a window allows through from the outside, so for us, that means the lower the better. BTW, clear glass has a SHGC of 0.84. So, yeah, LoĒ³-340’s going to lower those energy bills for sure.

  • LoĒ³-340 has a high Light-to-Solar-Gain ratio (LSG) of 2.17. This might not sound like something we like, but we do. Mostly because a high LSG means that our Low-E coating is working hard at being “spectrally selective.” Or, that it’s letting a good amount of visible daylight in, but still blocking the rays that cause heat.

  • LoĒ³-340 uses argon gas to achieve its super-low U-Factor of 0.25. We love this, because the lower a window’s U-factor, the more resistant it is to heat flow, which means we’re better insulated whether it’s hot or cold.

Filling the space between LoĒ³-340’s double panes with air would give it an already low U-Factor of 0.29 (ordinary double-pane tinted glass has a U-Factor of 0.48), but Cardinal went the extra mile and filled that space with argon gas to deliver the savings and comfort of a 0.25 U-Factor. It’s a year-round win!

If LoĒ³-340 sounds like something you want to know more about, we invite you to reach out any time. Our team will be happy to answer all your questions and even provide you with a free estimate.