Not long ago, a pair of Harvard scientists hit on an "aha" moment in the most unexpected place: while waiting in line at a post office.

Robert Shepherd and Filip Ilievski were trying to help the rest of their research team create a new generation of bendable rubbery robots called soft robots.

They already had a design that allowed their bendy robot to undulate, or move in a wavy motion. But they were looking for a design that offered more movement.

"We knew that nature already has a lot of quadrupeds walking around, and we already had this undulator design," Shepherd said. "We thought, oh, we could just map one onto the other and we would have an undulator and a quadrupedal crawler."

Unprepared for their moment of inspiration at the post office, Shepherd and Ilievski were forced to jot down their ideas on an envelope.

They unveiled their creation in the Proceedings of the National Academy of Sciences. Their team, headed by George Whitesides, has dubbed the invention the multigait soft robot.

Soft robotics, experts say, is the cutting edge of robot design and holds unimaginable promise for several reasons.

First, let's point out the obvious: These are not your grandparents' - or even your parents' - robots.

In other words, this ain't R2-D2.

The Harvard team's soft robot is a white, X-shaped device made of a rubbery polymer called elastomer.

The robot's motion is controlled through many tiny chambers in its body that cause it to move when filled with compressed air. The air is fed through tubes attached to the robot. "They've used a clever system of chambers and shapes, and when you apply pressure, you get the robot to move in predictable ways," says Barry Trimmer, who's developing soft robotics at Tufts University.

It can adjust itself enough to crawl through a gap 2 centimeters (0.79 inches) wide and insert itself into places where metallic or hard plastic robots could never go. It weighs only 1.5 ounces (42.5 grams).

The technology has mind-bending possibilities.

Imagine a tiny twisty robot crawling into your body so your doctor can perform a procedure without surgery.

Larger soft robots could be developed to assist elderly people with common tasks like opening doors, drawing a bath, or helping them stand or walk.

Or, perhaps such a robot could help search-and-rescue squads find victims trapped under rubble from a disastrous earthquake.

Soft robots could be useful in other ways too, like exploring other planets and bomb disposal.

Aside from research and development, this kind of technology is astoundingly inexpensive.

The materials used to create the Harvard robot cost about $5, Shepherd says. After the design was perfected, the prototype was manufactured in about two hours.

Special materials could be developed for different robots, depending on their tasks. Medical robots could be made of proteins, such as silk. Other robots could be built with materials that are biodegradable for convenient and safe disposal.

"It's becoming a major focus of robot research," Trimmer says. "There's increasing investment in Europe in building and developing soft material robots. The U.S. needs to think a lot more about this and put more resources into it."

The Harvard project was funded by the Defense Advanced Research Projects Agency, the Pentagon's research think tank.

But scientists still have some big hurdles ahead. One of the most challenging, Trimmer says, is designing a soft robot that is independent and autonomous.

The Harvard robot can't move without compressed air, which is fed through tubes attached to its body. "Usually, if you want to build a device to do something useful, you don't want it to be tethered," Trimmer says. "If you want it to travel somewhere, you don't want it to be trailing wires or tubes."

Scientists also hope to develop soft robots that are much larger and much smaller.

But don't expect soft robots to eventually replace the hard kind. As robots start to become part of everyday life, experts say, there will still will be a need for R2-D2s and C-3POs.

"Science is still trying to make really good hard robots - including humanoid robots," Trimmer says. "There's a huge legacy of hard robots out there, and they also can do a lot of things humans can't."