The (officially designated as the C650 Series ) is a premium line of fiberglass windows and patio doors designed for high-end residential durability and modern aesthetics. Built using a specialized pultrusion process that combines glass fibers with thermally-set resins, these windows offer the strength of steel with the low-maintenance benefits of vinyl. Because fiberglass expands and contracts at nearly the same rate as the glass it holds, the Ultra Series is exceptionally resistant to seal failure, warping, and cracking, even in climates with extreme temperature swings. Key Performance & Engineering Features