Why are katanas heavier? Because European medieval swords are all made of uniform spring steel. They spring back into shape when bent, this means you need less material, the blades can be longer, and this also means that, for longer blades, the swords can be lighter. Katanas, by contrast, have all of the hard steel at the edge, and the lower-carbon steels and even just straight iron at the spine. This means that katanas have to be thicker and heavier to be durable enough to use, because katanas, if they bend, don't spring back into shape, but they stay bent.