A compartment with water in it encased by some cold resistent matrial with a chamber of liquid nitrogen or some other really cold thing contained so that you could relase it into the water and it would expand to create a sort of sheild. there would be a heater inside to melt it back down so it could be reused. the cold stuff would be kept in a seperate pack so you could inject more after you melted the sheild. the water would expand so you build a 2nd wall 3 or 4 inchs above the first top and the first would be pushed up as the water expanded till it filled out the whole thing. Would be best suited to hand to hand combat. Bullets would blow it to peices. You can't turn kevlar on and off. The same idea could be used for a ice knife or body armor though the knife would have to be reinforced so it didn't snap in half.-- Wingmaster, Jan 09 2007 Ice formed rapidly in this fashion would be incredibly easy to break; blocks of ice that stop serious impacts are formed very slowly and are seriously strong, but flash-frozen ice would have a significantly weaker crystal structure. Furtmore, where are you going to get enough power for the heater in a hand to hand combat shield? Plugging in? Here's an idea for you; this would probably be easier to turn into a weapon than a shield. Perhaps you should figure out if you can flash freeze water with liquid nitrogen at high velocity; with tweaking, you may be able to create a nasty spray of ice-bullets moving just fast enough to cause serious problems to small groups of assailants. Even if you can't make it lethal, that just makes it a riot control weapon.-- killjoy57us, Feb 28 2007 a) What is needed here is not ice, but Pyecrete (frozen water with a small percentage of woodpulp). Huge work of fracture, probably much better as a bullet-proofed vest.
b) If you want to add liquid nitrogen to a closed compartment of room- temperature water strapped to your body, please can I watch from a distance?
d) You have overestimated the amount by which water expands on freezing.-- MaxwellBuchanan, Feb 28 2007 random, halfbakery