Supertensile Material is a goal in nanotechnology to make strong materials at the molecular level. For example, spider webs are very sturdy but limited due to spiders being the only thing that can make it. It so strong, that if we are to make the golden gate bridge out of it, it can support 100 times more weight than it does now BEFORE it "bends" or react to the weight.
So in short, nanotechnology scientists want to manufacture spider silk and use it in real world application, among other things.