The armour consists of material impregnated with liquid silica that has been modified using nanotechnology. It is designed as a flexible alternative to the current military armour, which consists of Kevlar material reinforced by heavyweight ceramic plates.

The American army hopes to use the liquid armour — which has been likened to the skin of cyborgs in films such as Terminator and RoboCop — in a new combat outfit that will enter service in 2010. British troops are also examining the concepts behind the armour, the technical name of which is shear thickening fluid (STF), for the Ministry of Defence’s Future Infantry Soldier Technology project.

“We can’t yet say STF will stop every bullet, but we are already seeing how it provides enhanced protection for less weight,” said Eric Wetzel, the co-inventor of the substance at the US Army Research Laboratory’s materials centre in Natick, Massachusetts.

A small British company, d3o Lab based in Hove, East Sussex, has already developed an STF-based foam that provides extra stiffening against impact in commercial products such as goalkeeper gloves, snowboarding shoes and ski suits. But the American armour, developed in conjunction with the University of Delaware, goes much further.

The silica nanoparticles in STF move around like a liquid under normal conditions, but when struck lock together in a solid lattice-like structure that lasts only as long as the impact.

A lightweight vest impregnated with STF has already been tested and has proved able to stop knife-stabs, fragmentation blasts, lower-power bullets and even hypodermic needles. At this level of development, it is suitable for staff such as police and prison officers.

The next stage is to strengthen the armour sufficiently to withstand high-velocity bullets and shrapnel from roadside bombs.

American and British officials are anxious to improve the effectiveness of body armour because of the constant stream of deaths and injuries in Iraq and Afghanistan.

Conventional Kevlar body armour with ceramic plate inserts has cut the death rate, but is heavy and unwieldy and leaves legs and arms vulnerable to severe wounds.

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