many legends surround japanese swords, the most frequent being that the blades are folded an immense number of times, gaining magical properties in the meantime. while blades folded hundreds, thousands, or even millions of times are encountered in fiction, there is no record of real blades being folded more than around 20 times. with each fold made by the maker, every internal layer is also folded, and so the total number of layers in a sword blade is doubled at each fold; since the thickness of a katana blade is less than 2 iron atoms, going beyond 20 folds no longer adds meaningfully to the number of layers in the blade. folding a blade only ten times will therefore create 1024 layers; 20 times will create 1,048,576 layers.