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A team of engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half. It's made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its sandwich structure, similar to that of corrugated cardboard, makes it more than 10,000 times as stiff as a solid plate of the same mass. The nanocardboard's unique mechanical and thermal properties are critical for its potential uses in microrobotic flyers, and for thermal insulators in microfabricated energy converters in which the material would need to recover its shape regardless of what deformations or temperatures it goes through. Shown here: A piece of nanocardboard balancing on an iris leaf.