Few parts of a building work harder than its envelope (also known as its facade). The envelope is the part of the building most visible from the outside—so it should be visually appealing—but it can also have the biggest effect on the well-being and safety of its occupants—so the envelope should be help heat and cool the building, allow light into it, and provide necessary structure. Too often, a building's envelope is more aesthetically striking than functional, or vice versa. A great building envelope, though, architecturally integrates all of its elements.