Advances in electrochromic coatings may bring us closer to environmentally friendly ways to keep inside spaces cool. Like eyeglasses that darken to provide sun protection, the optical properties of these transparent films can be tuned with electricity to block out solar heat and light. Now, researchers report demonstrating a new electrochromic film design based on metal-organic frameworks (MOFs) that quickly and reliably switch from transparent to glare-diminishing green to thermal-insulating red.