Secondary windows—also known as low-e storm windows, insulating panels, or secondary glazing systems—are a cost-effective, high-performance alternative to full window replacement for commercial buildings with old, inefficient windows. Secondary windows simply attach to the interior or exterior of an existing (i.e., primary) window for quick installation, resulting in improved occupant comfort, health and wellness, while reducing heating and cooling energy use by up to 20 percent. Further, secondary windows can achieve about the same performance as replacing windows with new high-performance models, but for as little as half the cost.