What is Low-E Glass?

To answer this, first let’s look at what low-E is.

Low-E is a very thin, almost invisible layer, applied to glass to increase its thermal efficiency.  Low-E stands for low emissivity. It is typically applied to glass in either one of two methods; pyrolytic or sputtered.  Pyrolytic low-E, also know as a hard coat, involves a process where tin oxide is baked onto the surface of the glass.  Forming a covalent bond with the glass, the resulting baked-on pyrolytic or hard coat low-E is extremely durable.  Alternatively, sputtered low-E makes use of silver oxide and is referred to as soft coat low-E.  Sputtered or soft coat low-E is applied in one, two, and three layers onto the surface of the glass.  Unlike pyrolytic low-E, sputtered low-E must be protected from humidity and contact.  Thus, sputtered (soft coat) low-E is applied to the interior surface of the glass that faces the sealed air space in a dual or triple glazed unit.

Now, those are all fancy, technical words, but what does that mean for you the homeowner?Low-E-window-diagram

Well for starters, it depends on where you live in the world and what your climate is like.  Depending on where you live, low-E is applied to different surfaces on an insulated unit; dual pane and/or triple pane glass.

Low-E is designed to deflect Ultra-Violet and infrared radiation.  In colder climates, the low-E is applied to the interior, inner-most surface to deflect heat back into the home, helping to reduce heating costs.  In warmer climates, low-E is applied to the interior, outer-most surface to deflect heat out of the home, reducing cooling costs.  The diagram to the right illustrates a dual-glazed insulated unit that is best designed for a warmer climate.  The low-E II denotes two coatings of low-E applied to the glass.

Choosing windows and doors that have low-E coating(s) on the glass can significantly reduce your energy costs each year.  A window or door’s energy efficiency is measured by its U-Value and SHGC ratings, which are directly effected by low-E.  When considering and comparing products that best meet your insulating needs, be sure to check these two ratings.




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