This Ball is made of colored, transparent plastic. It has 20 IR Diodes inside, which can emit continous (for Robocup Junior competition) or pulsed Infrared Light. Robots can detect the Ball easier with this.
Alternatively to Infrared Light, the Ball can also be tracked through it's blue color (for example with a camera).
For control of the IR Diodes the Ball is equipped with a small ATTiny Microcontroller.