Zorb ball is a double-sectioned sphere, with one ball inside the other with an air layer between. This acts as a shock absorber for the rider, damping bumps while traveling. Zorb balls are lightweight and made of flexible plastic. Many zorb balls have straps to hold the rider in place, while others leave the rider free to walk the zorb ball around or be tossed about freely by the rolling motion - water can be added inside, and this is commonly called a "water or aqua ride". A typical zorb ball is about 3 metres (9.8 ft) in diameter, with an inner zorb size of about 2 metres (6 ft 6.7 in), leaving a 50–60 centimetre (20–24 in) air cushion around the riders. The inner and outer zorb ball are connected by numerous (often hundreds) small ropes. Zorb balls have one or two tunnel-like entrances.