Are Foam-Filled Window Frames Better?

Vinyl and Fiberglass

• The U.S. Department of Energy (DOE) includes vinyl and fiberglass among materials that are good insulators for window frames. Vinyl provides more thermal resistance than other materials, such as metal. That’s because vinyl conducts less heat, so a vinyl window frame remains cooler in summer and warmer in winter than a metal frame. However, the composition of fiberglass makes it a better insulator than vinyl. Fiberglass consists of strands of fiber mixed with silica, or glass. The fiber content of fiberglass increases its ability to control heat conduction.

Foam-Filled Frames

• Standard vinyl and fiberglass window frames have hollow channels inside them, but foam fills those channels in insulated frames. The foam improves the insulating performance of both vinyl and fiberglass, according to the DOE. Foam also may improve a frame's structural strength by keeping it from bending out of shape due to slight shifts in a home's foundation.

Window Construction

• Nearly every part of a window contributes to its energy efficiency. Therefore, foam-filled vinyl or fiberglass window frames are only more energy-efficient than standard frames if other parts of the window are airtight. For example, there needs to be a tight fit between the windowpane and the frame to prevent cold or hot air from leaking through the frame in winter or summer. Ultimately, the performance of foam-filled frames is only as good as the quality of the construction of the entire window.

Efficiency Rating

• Foam-filled window frames, airtight panes and other design elements can produce windows with "R" values as high as 7, according to the National Academy of Engineering. By comparison, the NAE indicates that older, single-pane windows have "R" values as low as 1.2. The construction industry uses "R" values to rate the insulating properties of buildings and materials, and the higher the rating, the better a product's insulating performance. The NAE indicates that energy lost through poorly insulated windows represents about 30 percent of the energy used to heat and cool a building.