Learn about Low-E coatings, argon gas fills, and other glass technologies that improve window energy efficiency and comfort.
Low-emissivity (Low-E) coatings are microscopically thin metallic layers applied to window glass that reflect infrared heat while allowing visible light to pass through. There are two main types: passive Low-E (or hard-coat) is applied during glass manufacturing and performs well in cold climates by allowing some solar heat gain, while solar-control Low-E (or soft-coat) is applied in a vacuum chamber and is optimized to block solar heat in warmer climates. Modern triple-pane windows often use two Low-E coatings on different glass surfaces for maximum thermal performance, achieving U-factors as low as 0.15.
The space between glass panes is filled with inert gases that insulate better than air. Argon gas is the most common fill, providing about 30% better insulation than air at a modest cost increase. Krypton gas offers even higher insulating performance and is typically used in triple-pane windows with narrower gaps between panes. Some manufacturers offer argon-krypton blends that balance performance and cost. Over time, a small amount of gas may escape, but quality windows retain more than 90% of their gas fill for 20 years or longer.
Beyond Low-E and gas fills, other glass options include tinted glass that reduces glare and solar heat gain, laminated glass with an interlayer that blocks UV rays and reduces noise transmission, and tempered glass that is four times stronger than standard glass for safety applications. Our Glass & Coatings Explorer helps you understand how each technology affects energy performance, comfort, and cost so you can choose the ideal glass package for your windows.