Until last year, scientists were able to produce only paper-thick metamaterial sheets just large enough to cloak objects the size of a bacterium. Last June, John Rogers, a materials scientist at the University of Illinois, unveiled a metamaterial printer. "We can now bang out gigantic sheets of this stuff," he says, "though the grid designs need more work before these quantities will be practical." The sheets feel like plastic. For now, objects placed behind one of these sheets would just appear a little faded, since the design is still imperfect. "Losing an invisibility cloak would be a nice problem to have," Rogers says. "But creating one in the first place is the bigger challenge."