The zorbing is double-sectioned, with one ball inside the other with an air layer between. This acts as a shock absorber for the rider, damping bumps while traveling. Orbs are lightweight and made of flexible plastic, as opposed to the rigid plastic, for example, of a hamster ball. Many orbs have straps to hold the rider in place, while others leave the rider free to walk the orb around or be tossed about freely by the rolling motion. A typical orb is about 3 metres (10 ft) in diameter, with an inner orb size of about 2 metres (6 ft 7 in), leaving a 50–60 centimetre (20–24 in) air cushion around the riders. The plastic is approximately 0.8 millimetres (0.03 in) thick. The inner and outer orb are connected by numerous (often hundreds of) small nylon strings. Orbs have one or two tunnel-like entrances.