The curved shape that a yarn length, whether stationary or in forward motion, forms in space when it is made to circulate (i.e. whirl) at a fixed or varying radius around an axis. Note 1: The forward motion of the yarn length is commonly called the yarn delivery speed. Note 2: Balloons commonly occur when a yarn length circulates a package, mainly out of contact with the package, during over-end twisting, winding and unwinding operations (e.g., uptwisting, downtwisting, ring spinning, yarn doubling or folding, see diagram). Balloons can also occur when yarn lengths whirl free of lateral constraints (c. g., air-jet spinning). Note 3: Balloons may be single or multiple and their size, basic shape and angular velocity are system and the rate of twisting. These factors control the determined by the geometry of the on. The forces are centripetal, coriolis, air-drag and yarn balance of forces producing the balloon, shape and angular velocity are package tension. Other factors that may influence balloon sizes of the yarn and the presence of balloon size, ring size, traveller weight, linear density, hairiness control rings or balloon separators.