Most materials can be expected to have a positive Poisson's ratio, i.e. to shrink in x- and y-direction when they are stretched in z-direction and vice versa. Some materials and constructions, however, show a negative Poisson's ratio - starting from crystals, ceramics etc. to foams or man-made structures. Besides the basis interest in these structures, they can offer other interesting properties, such as shear resistance or sound absorption, allowing for their use in different fields of application.