Doors and windows are the greatest contributors to heat and air loss in a home, so the energy efficiency and insulating abilities of the products are important considerations. Fiberglass windows are energy efficient, versatile and strong, but they also have a few disadvantages.
Time
The lead time of a fiberglass window is long because the production process is labor intensive. Every fiberglass window is a custom window. Vinyl windows can be installed as soon as one week after the order is placed, but fiberglass windows take longer. With tight schedules on the job site, this longer lead time can be a major concern.
Cost
Fiberglass is the most expensive replacement window frame type. Fiberglass windows have an expensive manufacturing process and are not widely available. The small number of fiberglass window manufacturers lowers the supply, also increasing costs. Shipping long distances can also significantly raise costs.
Color Fading
Fiberglass windows are available in only a few colors, and the darker colors tend to fade over time. However, unlike vinyl replacement windows, fiberglass windows can be painted.
New Process
Because fiberglass windows are a new offering in the marketplace, manufacturers are still refining the process and long-term stability of the product is unknown. Claims made about the longevity of the window frames are estimates at best.