Spider silk – the protein fiber spun by spiders to make webs, nests, cocoons, and wrapping for prey that they stash away – is a remarkable substance. Its mechanical properties combine high tensile strength and high extensibility or ductility. This allows spider silk to absorb a lot of energy before breaking. It is stronger than steel, but not as strong as Kevlar, for example. On the other hand, it is tougher than either.