What Is Low-E Glass and How Does It Work?

Low-E (low-emissivity) glass has a microscopically thin, virtually invisible metallic or metallic-oxide coating applied to the glass surface. That coating selectively reflects infrared (heat) radiation while still allowing visible light to pass through — which is why it doesn't noticeably darken a room the way tinted glass does.

Two manufacturing types

Hard-coat (pyrolytic) Low-E is applied during glass manufacturing at high temperature, bonding it directly into the glass surface — durable, but generally a less effective insulator than soft-coat.

Soft-coat (sputtered) Low-E is applied in a vacuum chamber after the glass is formed, in multiple thin layers. It performs better (lower U-factor, better solar control) but must be sealed inside an insulated glass unit rather than exposed to air, since it's less durable on its own.

Spectrally selective coatings

Higher-end Low-E products use spectrally selective coatings, engineered to block a larger share of infrared and ultraviolet wavelengths while maximizing visible light transmission — useful for Indiana's combination of hot summers and cold winters, where you want both heat rejection in summer and heat retention in winter without losing daylight.

See our page on energy-efficient windows for how Low-E fits into the broader U-factor and SHGC picture.