Polyvinyl chloride
The tubes are usually constructed and then partitioned with separate chambers to reduce the effect of a puncture, each with a valve to add or remove air and more recently pressure release valves. Larger boats (7m+) have six or more chambers with a valve and pressure release for each chamber. The more chambers a boat has the more redundancy the boat is considered to have. This is because if only one chamber is damaged then the impact the damage has on the boat is much less. In recent years tubes tend to be fitted with both valves and pressure relief valves as temperature increases the air inside the tube expands and the pressure release valves will open. This prevents the tubes bursting from overpressure. Common materials for the tubes are Hypalon and PVC (Polyvinyl chloride), though some manufacturers use PU (Polyurethane).