Our Fiberglass windows, made by Pella, are a wonderful option for homeowners who are looking for lower maintenance choices. Pella Impervia® products are incredibly energy-efficient and lo-maintenance. Made of patented fiberglass composite called Duracast®, these products can take almost anything; including extreme weather, impacts, and sea air. But the real strength of Pella Impervia® products in their competitive Price. Just another way Pella takes outstanding value to the extreme.