auxetics

Auxetic metamaterials are a type of metamaterial with a negative Poisson's ratio, so that axial elongation causes transversal elongation (in contrast to an ordinary material, where stretching in one direction causes compression in the other direction). (Wikipedia, CC BY-SA)

L'auxétisme (du grec auxein, s'étendre) est le fait, pour un matériau, de posséder un coefficient de Poisson négatif. (Wikipedia, CC BY-SA)