Graphene, the monolayer all-carbon supermaterial has been touted as stronger than steel, having marvelous electro-optical properties and having the potential to revolutionize engineering, computing and electronics. But, not so fast, Rice University theoretical physicist Boris Yakobson and his colleagues in China. Writing in the journal Nano Letters, the team says that less-than-perfect sheets of the material have an unexpected weakness that apparently makes them only half as strong as predicted. The team has calculated that flaws in the otherwise endless chicken wire array of hexagons, that allows seven-membered carbon rings to appear, inevitably occur at grain boundaries in graphene and so under tension, polycrystalline graphene is expected to break under lower loads than the pristine material would. Yakobson explains that, If you need a patch of graphene for mechanical performance, you’d better go for perfect monocrystals or graphene with rather small domains that reduce the stress concentration.