Windows and their frames can be a significant contributor to the use of energy in your home — either saving it or unnecessarily expending it. Environmental factors to consider when choosing your window frames include energy and resource issues.
•Low-conductivity frame, sash, and spacer materials conserve energy by controlling heat gain and loss
•Durable, low-maintenance window assemblies reduce replacement costs — and if made of recycled-content they also conserves natural resources.

Aluminum is a metal whose properties make it ideal for strength yet poor for energy efficiency. Aluminum frames easily conduct heat faster than other options, especially if not well insulated with a thermal break. They are more prone to condensation and corrosion, leaving a dull pitted appearance. Deterioration can be avoided through anodizing or coating, but they can not be painted. Thermal resistance can be improved by placing continuous insulating plastic strips between the interior and exterior of the frame.
Wood frames have higher R-values and are not affected by temperature extremes. Wood is generally warm to the touch even in cold winters and at room temperature in the hot summers. They usually do not promote condensation. Wood frames are generally from pine, often of old-growth sources, and require significant maintenance, such as periodic painting or finishing, to prevent swelling, warping, sticking and rotting.
If choosing wood window frames, look for FSC-certified wood. Currently, only a limited number of manufacturers use FSC-certified wood as a standard frame material. Look for EnergyStar and/or an NFRC certification with a U-factor of 0.25 or lower.
Vinyl window frames, are made primarily from polyvinyl chloride (PVC). They offer many advantages and disadvantages. Vinyl frames are durable, energy efficient and available in a wide range of styles and shapes. They have moderate to high R-values, are easily customized, are competitively priced, and require little maintenance.
They do not have the inherent strength of metal or wood, so larger-sized windows are often strengthened with aluminum or steel reinforcing bars. They are made of a nonrenewable petroleum source. There are environmental issues associated with PVC, including chlorine in the manufacture, offgassing during use and disposal through incineration. Recycled content vinyl is considered by many to be a more sustainable material. If choosing recycled vinyl look for an NFRC certification with a U-factor of 0.20 or lower.
Fiberglass frames are relatively new and are not yet widely available. They are made from a composite of polyester resin and glass fibers. They have some of the highest R-values, with excellent insulating capabilities. They are known to not warp, shrink, swell, rot, or corrode. To ensure holding up to the weather, Fiberglass windows have factory applied, baked-on coatings which can be repainted. Fiberglass is stronger than vinyl and has lower maintenance requirements than wood. Some fiberglass frames are hollow, while others are filled with foam or fiberglass insulation. Fiberglass is considered a combustible material, so there are limits to the size and range of applications where they may be used. Look for an NFRC unit U-factors of 0.30 or lower.