Flexible body armor is currently in use by US and Canadian skiers. This armor is normally flexible, but reacts automatically to impact, hardening into a protective layer around the skier. The armor is made from a "material [that] exhibits a material property called "strain rate sensitivity". Under normal conditions the molecules within the material are weakly bound and can move past each with ease, making the material flexible. But the shock of sudden deformation causes the chemical bonds to strengthen and the moving molecules to lock, turning the material into a more solid, protective shield."This effect is quite like the cornflour putty you can create in this experiment .