Well, you can fold a raised corner in any sheet material. Turn up the edge of each side of the corner, make a diagonal fold in the corner (this will tend to form of its own accord as you turn the edges up). Fasten the resulting upper triangular flap to one edge or the other; a paper clip, for instance?
However, you may find that a structure like this will cause fracturing of the film in the corner, due to the sharp folds that result.
Experiment with a sheet of paper.
You can make these structures for non-right-angled corners, too, only the resulting 'triangular fold' flap isn't quite as convenient as it is with the right-angled corner (as the corner angle increases beyond 90 degrees, the flap gets narrower, and rises above the turned-up edge).