Measures how much air can get through a window or door. The lower the number, the better.
A window spacing option used in lower end windows. Tends to conduct temperatures more from the outside to the inside and generally comes with a lower warranty.
Common window insulator. It is nontoxic, colorless, odorless and tasteless gas. It is 6 times denser than air, and drastically reduces heat loss between the panes of glass.
Window style commonly used in basements, porches and spaces close to the ceiling. Window operates like a casement except it is hinged at the top and always swings out.