Window Technologies

Operator Types

Traditional operable window types include the projected or hinged types such as casement, awning, and hopper, and the sliding types such as double- and single-hung and horizontal sliding. This section on Operator Types describes how these typical windows work.

Glazing Types

Traditionally, windows have been made from clear glass, but advanced technologies have significantly improved the thermal performance of glass. This section on Glazing Types describes some of these technologies.

Gas Fills

Gas fills improve the thermal performance of insulating glazing units by reducing the conductance of the air space between the layers. This section on Gas Fills describes the thermal performance benefits of adding gas to an IGU.


The layers of glazing in an insulating unit must be held apart at the appropriate distance by spacers. Warm edge spacers have become increasingly important as manufacturers switch from conventional double glazing to higher-performance glazing. This section on Spacers describes the different spacer technologies.

Frame Types

The material used to manufacture the frame governs the physical characteristics of the window, such as frame thickness, weight, and durability. It also has a major impact on the thermal characteristics of the window. This section on Frame Types describes the performance impact of different frame materials and how they influence the total window performance.

Emerging Technologies

Most of the emerging glass technologies are available or nearly on the market. These include insulation-filled and evacuated glazings to improve heat transfer by lowering U-factors.

A variety of window technologies can improve window energy efficiency, including gas fills, low-E coatings, and high-performance frame options. How these technologies affect a window’s energy performance depends on the sum of all parts. This is where whole window energy ratings help, accounting for the combined effect of glazing, spacers and frame (thermally improved). The only reliable way to determine whole-window energy properties are the ratings certified by the National Fenestration Rating Council (NFRC). In most jurisdictions across the United States, building energy codes require that windows bear the NFRC label so that the code compliance of their energy ratings can be verified.