French doors were first developed in the 17th century to bring more light into dimly lit homes, in the era before electricity. The solution was to design a door that looked much like a window, with glass that extended for most of the door’s length. While many French doors are still designed with the grid pattern they’re most known for, they are also available in grid-free designs to allow in as much light as possible.
Whether they swing inward, or outward, French doors are exceptionally energy-efficient and are often manufactured with dual pane glass to reduce air leaks and heat loss. In comparison to older patio doors, modern French doors are exceptionally adept at keeping your home at a comfortable temperature all year round.