Auxetics
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Auxetics are materials that become thicker perpendicularly to the applied force when stretched. They have a negative Poisson's ratio, that is, they get thicker and not thinner when stretched. Materials of this sort are expected to have interesting mechanical properties such as high energy absorption and fracture resistance which may be useful in applications such as packing material, knee and elbow pads, robust shock absorbing material, and sponge mops.
The term auxetic is derived from the Greek word auxeos which means, that which can expand. Auxetic materials can be single molecules, or a particular structure of macroscopic matter.
Auxetic materials are quite new. The earliest published example was in Science in 1987, "Foam structures with a negative Poisson's ratio" by R.S. Lakes. The use of the word Auxetic to refer to this property was probably begun in 1991.
Auxetics is also the name of a technology company based in Sheffield, England [1].