Low-E coating
low-emissivity coating · “low-ee”
A microscopically thin metallic layer baked onto window glass that lets daylight through but reflects heat. It's the single biggest driver of how a window performs.
What it means for you
Two windows can both say “double-pane” and perform nothing alike — the Low-E package is usually why. In an NC summer it's most of the comfort you're paying for, and skipping it is the one downgrade you'll actually feel.
Where you'll see it
A line on the NFRC sticker, a glass-package upgrade on your quote, and the centerpiece of most in-home demos (the heat-lamp box).
Don't be fooled
Every brand renames the same physics — “Comfort 365,” “SmartSun,” “Low-E 366.” Ask for the U-factor and SHGC numbers, not the trade name.
Also sold as: Comfort 365 · SmartSun · Low-E 366
Related terms
Reading this on your own quote?
Run the 30-second check — where your number lands against real NC ranges, plus the red flags.
Check my quote →