Hard metal robots are fine and good for building cars and exploring Mars, but when it comes to gripping fragile objects or mimicking human limbs, soft machines are best. The problem: Today’s soft robots are very delicate, and small rips or punctures could destroy them. To combat this, researchers have built soft robots with a material that, with a little heat, can reassemble itself after being damaged. The robots get this healing factor from their construction. They are made entirely of a synthetic material called an elastomer, short for “elastic polymer.” When heated, the molecular bonds that keep the elastomer together loosen and begin to reform back to their original cubelike shape. Remove the heat, and the bonds resolidify. A little over an hour after being damaged, the material was almost completely healed, and 24 hours after cooling, the only evidence was a small scar. The robots could withstand cuts and stabs, and achieved nearly full performance once healed, the team reports today in Science Robotics. Even after two healing cycles, the grabber could still grab and the muscle could still flex.