Today we enter the world of auxetics, materials that, when stretched, expand perpendicular to the applied force.

Wait, what? This:

It sounds counterintuitive at first (at least it did for me), but this type of hexagonal material seems familiar for whatever reason. These materials have a negative Poisson’s ratio—thus their expansion when stretched. Most materials have a positive Poisson’s ratio, since they thin as they stretch. According to one article I’ve read, Poisson’s ratio is defined as minus the transverse strain divided by the axial strain in the direction of stretching force…Poisson’s ratios, denoted by a Greek nu, n, for various materials are approximately 0.5 for rubbers and for soft biological tissues, 0.45 for lead, 0.33 for aluminum, 0.27 for common steels, 0.1 to 0.4 for cellular solids such as typical polymer foams, and nearly zero for cork.” This article was written back in 1987, back before auxetic materials had been thoroughly examined. Now there are models that have just been put out to help explain the behavior of this weird stuff that occurs naturally in some rock, bone, and, apparently, paper.

More info here, here, and here. Cool, huh?

Today’s song: Mashina by NikitA