Fiberglass windows have to sit flush within the frame. More often than not, custom modifications must be made. A professional window contractor is familiar with the installation process. The primary benefits of installing fiberglass windows are their durability and strength. Fiberglass window frames are the strongest available. They have a fantastic lifespan (up to 20 years), which makes them a very popular option in areas with harsh climates. Fiberglass is also energy efficient, so the high cost of installing this type of window eventually pays for itself because you’ll save on heating and cooling expenses down the line. Fiberglass requires very little maintenance. The material can be painted, but it’s not required.