Snow Tubing is an individual activity where participants ride inflatable tubes down snow-covered hills.

Snow tubing is a wintertime activity similar to sledding where participants ride an inflatable inner tube down a snowy hill or slope. The low amount of friction between most tubes and snow allows participants to reach high speeds while riding. It is also possible to tow a tube through the snow behind a snowmobile. This is similar to towed tubing on water, only the watercraft is replaced by a snowmobile and the water with snow-covered ground.

To use an inflatable inner tube to slide down a snowy hill or slope, using gravity to propel riders to the bottom.

Inner Tube
Winter Gear

Because of the circular shape of snow tubes, controlling the course and speed of a tube while riding on snow is extremely difficult. While a sled rider can drag their arms on the snow to brake or steer to a degree, attempting this on a tube will often cause the tube to spin. This lack of control has led to injuries, some serious, when riders have struck obstacles such as trees while tubing on snow.

Some ski resorts offer courses devoted solely to tubing. Such courses often have slopes or barriers on the periphery to guide the tubes along a safe course. Motorized pulley towlines are often used to tow riders and their tube back to the top of the course after riding to the bottom.

http://en.wikipedia.org/wiki/Tubing_(recreation)#Snow