When ordinary materials are pulled from side to side, the top and bottom tend to shrink towards each other. It's the behavior of squeezing a balloon: some part comes out somewhere else.
Auxetic materials behave in ways that are surprisingly opposite of ordinary. https://en.wikipedia.org/wiki/Auxetics When the sides are pulled away from left to right, the top and bottom actually expand higher and lower.
From a shopping bag I folded a pattern similar to the offset zig zag of the auxetics diagram, but interestingly there was little movement in one direction, while there was great flexibility in expanding in the other. The expandability looked like it might be useful when used in a face mask to cover different sizes of faces, but sealing the edges is a challenge.
Here is a brief video to observe the behavior of this piece.
