U.S. and Canadian slalom skiers are wearing lightweight, flexible protective gear made from a new material (d3o) that hardens into armor when it's crashed into.
Normally, skiers wear hard arm and leg guards to protect themselves from poles along the slalom run. But the Colorado-based skiwear company Spyder created racing suits with d3o along the shins and forearms, and the suits caught on.
The exact chemical composition of d3o is a trade secret, but it's made by combining a viscose fluid and a polymer, then pouring the liquid d3o into a mold that matches the shape of the body part needing protection.
According to a New Scientist article,
"The resulting material 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.