I have wondered for a while what these things really are. I have played with the idea of building a 1:1 bunk in a guest room for the hell of it (I would first have to clear it with the XO - my wife.) I don't think they are just plain curtains as they seem to be fairly uniform, compact, seem to accordion closed, have a flat leading edge, and follow a track on the top and the bottom of the bunk opening.