Stretching, reversed

Early this week, Northwestern Physics undergraduate Zachary G. Nicolaou reported on some peculiar material properties in Nature Materials. What makes these materials unique is how they respond to tension and compression. For most materials -- metals, plastics, ceramics -- the typical response is to extend and contract, respectively. For Nicolaou's materials, the opposite is true. That is, when these materials are tensions, they contract, and when they are under compression, they expand...