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Thin layers are commonly used in a wide kind of industrial products(from everyday packaging to airplanes) and are also frequently found in biologicalsystems. The mechanics of thin sheets is rich and complex, with strong geometrical non-linearities leading for example to the intricate folds and singularities that we canobserve in a crumpled sheet of paper. But here we show that the fracture path in thinsheets can follow remarkably regular geometrical path. We have observed crack paththat evolved from an initial notch a few millimeter wide into a logarithmic spiral crackpath that reached a meter in diameter. We present a model that explains the impressiveregularity of this crack path.