Journal

What Is Low-E Glass?.

Low-E glass is window glass coated with a microscopically thin layer of metal oxide that reflects infrared radiation while letting visible light pass through. The coating cuts the heat the window loses in winter (keeping warmth inside) and the heat it gains in summer (keeping warmth outside), without darkening the view. Modern energy code basically requires Low-E on any residential window.

Updated May 30, 2026

How it works.

Heat moves through a window three ways: conduction through the frame, convection through air gaps, and radiation through the glass. The Low-E coating addresses the radiation path. It reflects long-wave infrared back toward whichever side it came from, while staying transparent to short-wave visible light, so the room stays bright but the heat stops at the glass.

The coating is paired with an insulated glass unit (typically two panes with argon gas between) so it works inside a sealed cavity. Position matters: a coating facing the cavity side of the outer pane optimizes for cold climate (keeps warmth in); a coating facing the cavity side of the inner pane optimizes for hot climate (keeps heat out).

Hard-coat versus soft-coat.

Hard-coat Low-E (pyrolytic) is applied while the glass is still molten and bonds into the surface. It is durable, can be cut and tempered after coating, and survives uncoated cavity exposure. Lower performance: typical emissivity 0.15.

Soft-coat Low-E (sputtered) is applied to cooled glass in a vacuum chamber. It is more delicate (must stay sealed inside the IGU) but performs significantly better. Typical emissivity 0.04, plus better visible light transmission. Soft-coat is the standard for residential new construction; hard-coat is used in storm windows and secondary glazing.

Common questions.

Does Low-E glass make the room darker?
Not noticeably. The coating reflects infrared (heat) while letting visible light pass through. A typical Low-E IGU has visible light transmission around 70 to 75 percent, comparable to standard double-pane without the coating.
Is Low-E glass worth the cost?
Yes, on any new construction or full window replacement. The energy savings pay back the modest premium within a few years and the comfort improvement (no cold spot near the window in winter) is immediate.
Can Low-E coatings fail?
Soft-coat Low-E depends on the IGU seal staying intact. If the IGU seal fails and moisture enters the cavity, the coating can degrade over years. Hard-coat is more robust but lower performance.

Project in motion

Specifying Low-E for your project?

Crateworks windows ship with soft-coat Low-E in argon-filled IGUs as standard. Send your project for the full glass spec.

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