Exterior folding doors
Interior Doors and their classification of way of opening : Exterior Folding Doors
Quote from Article entitled Interior Doors and their classification of way of opening:
When you think of what interior doors to choose, pay attention to the fact that rolls can be upper, lower, upper and lower. A door, which are set up with an upper roll, looks more exquisite but it can swing a little in a draught. Double-rolled doors are the most reliable and durable.
The full version of the article can be found here.