Conventional paper is made from cellulose, a crystalline polymer of glucose that is the primary component of plant cell walls. At the nanoscale level cellulose can be extremely strong, and the individual fibers are capable of withstanding more stress than glass fibers or steel wire.

“But paper processing generates relatively large cellulose microfibers riddled with defects that can break apart under stress. That leaves most commercial paper with a tensile strength that tops out at about 30 megapascals (MPa),” says Lars Berglund, a lightweight structures engineering expert at KTH Royal Institute of Technology, to ScienceNOW.

In order to make the paper tougher, Berglund and his colleagues kept the cellulose fibers small, according to ScienceNOW. They managed to do so by breaking down wood pulp in water with a combination of enzymes and mechanically beating it further. The result – pulished in the current issue of the American Chemical Society´s magazine Biomacromolecules – is a paper with a tensile strength double than that of cast iron.