'Impossible' material would stretch when compressed - New Scientist - New Scientist

'Impossible' material would stretch when compressed: Their theoretical design involves a row of four "particles" – each made of groups of molecules – that attract each other to varying degrees. The force attracting the two inner particles is weak, so that pulling on the material breaks that bond. "As soon as that happens, the outer particles attract each other more," says Motter, so overall the material compresses. If this material is squeezed, though, the two inner particles are brought close enough together to reform the weak bond – and the material can expand.