Silk — one of the strongest natural materials known — has a long history of use in combat: Legend has it that Genghis Khan once issued tightly woven silk vests to his horsemen as protection against their enemies' arrows. Researchers have now taken silk one step further, and developed a fabric made of silk proteins that is strong enough to stop a bullet. Their ultimate goal: To give a person a layer of bulletproof skin. Here, a brief guide to this breakthrough:

How did scientists develop this fabric?
They genetically modified goats to produce milk that contains the same protein that spiders use to make silk. Scientists then extracted the silk proteins from the goats' milk and used them to weave a kind of genetically modified silk. Finally, the material was cultured with human skin cells that, after about five weeks, created a tough, flexible, living material.

Is it really strong enough to stop a speeding bullet?
Almost. Tests show that the material is strong enough to stop a slow-moving bullet, but not a speeding bullet fired from a .22 caliber rifle, which is the standard for today's bulletproof vests. Researchers hope that further refinement will create tougher materials that can stop a bullet as consistently as garments made with bulletproof Kevlar.

Could we someday see a human with bulletproof skin?
It's possible with genetic manipulation, say the researchers. "Imagine a spider silk vest, capable of catching bullets, the modern-day equivalent of Genghis Khan's arrows," says inventor Jalila Essaidi, as quoted in the Daily Mail. "Now, let's take this one step further: Imagine replacing keratin, the protein responsible for the toughness of human skin, with this spider silk protein. Science fiction? Maybe..."

Sources: Daily Mail,, Huff. Post