Solar Innovations. The Mulled Window and Door System joins operable windows and swing doors into one cohesive system without the addition of rafters and framing, the company says, allowing for consistent, minimally interrupted sight lines. Specifiers can integrate awning, casement, fixed, tilt-turn, and egress windows in the same unit, and in-swing and out-swing units can be used within the same system. The system is pending Energy Star certification, with a 1 1/2- to 1 3/4-inch insulated, triple-pane, low-E glass offering a 0.34 U-value and 0.25 SHGC. Duracron and anodized exterior finishes are available in a range of colors. 800.618.0669..