A new material inspired by mussels is flexing its muscles. It can stretch without snapping and repair its own molecular bonds, so it could be useful in robot joints that lift heavy objects, or for packaging to protect delicate cargo from accidental falls. Mussels and some other molluscs hang onto solid surfaces using an adhesive protein and tough, plasticky fibres, which are extremely strong and can repair themselves when a few molecular bonds within them are broken. For a mussel, these stretchy yet strong fibres come in handy when a wave hits. Megan Valentine at the University of California, Santa Barbara, and her colleagues created a plastic with these same properties by mimicking the chemistry the mussels use.