There is a variety of non-metal framing materials for windows including, wood, wood with metal/vinyl cladding, vinyl, hybrid, and composites.
Does frame material type matter?
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. The window U-factor, as given on the NFRC certified rating or label, incorporates the thermal properties of both the frame and the glazing. Since the sash and frame represent from 10–30% of the total area of the window unit, the frame properties significantly influence the total window performance.