A new "skin" that changes shape at the push of a button could reduce the drag forces on aeroplanes or ships, making them faster and more fuel efficient, say US researchers.

Dr Othon Rediniotis and colleagues at Texas A and M University say the active coating can reduce the drag forces on an object in motion up to 40%.

"Aircraft drag reduction is becoming, again, a serious research issue."

As air or water flows over an object, it creates tiny pockets of turbulence that slow the object down.

In recent years, designers have roughed things up, adding tiny, immobile riblets to skins.

The riblets break apart the random formation of turbulent pockets and create specific, controlled areas of turbulence that engineers can use to their advantage.

Passive riblets, which can be found in the full-body swimsuits worn by professional swimmers, use the same principle to reduce drag by 5 to 7%.