A strange material may make protective helmets more so

ANYONE WHORAT has experimented as a child with maize starch and water knows about shear-thickening. A mixture of these substances is easy to stir slowly, but solidifies when you speed the stirring up, only to liquefy again when you stop. It’s fun. But it may also be important. For years, people have been trying to apply the principle to armour. Now, it seems, one group has succeeded. The result will not stop a speeding bullet. But, incorporated into a helmet, it might save the wearer from concussion.Construction workers, soldiers and sportsmen and women all wear safety helmets that contain impact-absorbing suspension systems based on foam pads or webbing straps. Eric Wetzel of the United States Army Research Laboratory and his colleagues propose replacing these with fabric tubes containing a shear-thickening material that the lab has developed. These tubes, which behave like viscous, speed-sensitive bungee cords, are known as rate-activated tethers, or s.