Deconstructing the auxetic behavior of paper

Why does the thickness of paper increase when its stretched?

Prateek Verma / 26 January 2014

polymers materials auxetic metamaterials paper

Did you know that the paper you write on increases in thickness when you stretch it? It is imperceptible to human eye though, so unless you are an alien with supervision awestruck by what humans are achieving through science, please don't start stretching the first sheet of paper you can find on your desk. The first piece of paper you can find on your desk, I must say now, probably does what I am telling you. Can you think of anything that expands upon stretching? Almost every material we use and come across in our daily lives, metals, plastics, and ceramics, contract upon stretching. Very few things can expand, and are called auxetic. Auxetic materials contract upon compression too! Again, don't start beating that paper. Auxetic behavior is extremely rare in naturally occurring materials and has only gained substantial recognition and synthesis efforts in the past two to three decades. That should be termed as a 'recent' development, given the very fundamental nature of the properties it effects or stems from. In my PhD thesis, I described why paper increases in thickness when it is stretched. In great detail. I will save you some time, and tell you now that it has to do with the wavy fiber structure of paper. Many different varieties of paper were examined. Some paper was even created in lab. We didn't stop there. We thought of doing this to other fiber networks and see if they can be made remarkable. Clothes, felts, even muscles, are fiber networks, by the way. We published a paper on paper, which should be less of a torcher reading than the thesis.