Window FramesA window's frame can be made out of aluminum or another metal, composite, fiberglass, vinyl or wood.All have their advantages and disadvantages, but the U.S. Department of Energy (DOE) recommends vinyl, wood, fiberglass or composite. (Aluminum is easily heated, so it isn't a great insulator.) Wood has efficiency problems due to expansion and contraction, so consider aluminum- or vinyl-clad windows. But if you choose vinyl, consider an insulated version, depending on your climate and house requirements, for better thermal insulation.