Metamaterials are already showing promise, as the building blocks to real-life invisibility cloaks; that's because the composites let electromagnetic waves flow around them, instead of reflecting 'em back. Darpa's "Asymmetric Materials for the Urban Battlespace" program goes way, way beyond mere invisibility, however. "Asymmetric, or 'one-way,' materials will support basic unit operations such as raids, cordon and search activities, snap checkpoints, and fire fights... Friendly forces will be able to see through [one of these new materials] and shoot through it, but hostile forces will not." Such shields will also have "the ability to 'self-heal' if necessary."