A hula hoop is a toy hoop that is twirled around the waist, limbs or neck. The modern hula hoop was invented in 1958 by Arthur K. "Spud" Melin and Richard Knerr, but children and adults around the world have played with hoops, twirling, rolling and throwing them throughout history. Hula hoops for children generally measure approximately 71 centimetres (28 in) in diameter, and those for adults around 1.02 metres (40 in). Traditional materials for hoops include willow, rattan (a flexible and strong vine), grapevines and stiff grasses. Today, they are usually made of plastic tubing.