There are two types of boating tubes or ski tubes. There is the partially covered towable tube, and the fully covered towable tube. There are various sizes designed to pull one rider or multiple riders. Tubes are rated as 1 person, 2 person, 3 person, and 4+ person towable tubes. The person rating represents maximum number of adult riders. Some tubes can handle more riders if, for example, on a 2 person tube, one is an adult and 2 are kids. For safety reasons, on larger 3 and 4+ person tubes, always have an adult rider on the tube with the kids. If a larger tube flips and a kid gets trapped under the tube, that adult can quickly assist.