Composite Window Frame
Composite window frames, also called engineered wood frames, are made from a variety of materials, including wood, wood fibers, metals, plastics, and a binding agent such as glue.
Like when shopping for any other window type, look for windows with other energy efficiency features, such as multiple panes, argon-filled, and low-E coatings. Since composite window frames are made of various materials, checking with the manufacturer as to the nature of those products would also be in your best interest. Often, composite window frames can be fabricated using reclaimed wood fibers or recycled plastic.
The insulating value of windows is often rated by the whole window U-factor and the lower the value, the better. Energy Star rated windows should have a U-factor of 0.27 Btu/hr-sq ft °F or less for Northern climates.
While the embodied energy of composite may be higher than solid wood, composite can be resistant to moisture and require less maintenance over time.
Early window frame materials included wood, iron, and lead. Of those, wood is still used today, and metal frames have graduated to aluminum, stainless steel, and coated steel, with insulation breaks to cut heat loss. Lead is no longer commonly used in window frames.