A castor includes a wheel support and at least one roller mounted on the wheel support. The at least one roller has a peripheral portion provided with a hollow air chamber which is provided with a plurality of hollow air columns. One of the hollow air columns is provided with an air inlet. The at least one roller is made of soft material that is made by a blow molding operation. The soft material is initially made into a tubular blank by a blow molding machine. A gas is then filled into the soft material to blow and shape the soft material in a die at a high temperature to form the at least one roller. The at least one roller is then stripped from the die.