Cork traditionally forms the base of a feather badminton shuttlecock.
A feather shuttlecock has a rounded cork tip covered with a thin layer of leather or synthetic material. Sixteen feathers are inserted into the cork and secured to create the distinctive cone shape used in formal badminton.
Cork is valued because it is light, resilient, and able to provide a consistent striking surface. The feathers create aerodynamic drag, allowing the shuttlecock to slow rapidly after being hit and to orient itself cork-first during flight.
Synthetic shuttlecocks use a plastic or other manufactured skirt instead of natural feathers, but their base may still imitate the shape and playing properties of a cork-tipped shuttle. The cork answer therefore applies to the traditional feather design, not every modern practice shuttle.